Idle Air Control Valves - Why I'm Not a Fan!
Discussion
Given my recent frustrations I can absolutely see now why the MBE system from Powers Performance does not use an idle air control valve, this takes be right back to when I was taught how to tune carburetor fed engines by the very knowledgeable old boys I worked with years ago, these very experienced mechanics relentlessly drummed into me the following lesson....
"All vacuum leaks must be absolutely eliminated before you start the tuning process"
This rule applies to all spark ignition internal combustion engines, it's really irrelevant if it's fed by a carb or injection, it's fundamentally still very much just a spark ignition internal combustion engine, these old boys I worked with really were very insistent on this point and of course it makes perfect sense, so it's stayed with me all these years
Now consider this.... it doesn't matter if you're running a idle air circuit on a carb, a stepper motor as used on the 14CUX, or the supposedly far more sophisticated PWM controlled infinitely variable rotary Bosch Idle Air Control Valve as used on the Canems system, the truth is they are all really just vacuum leaks!
Now let me take you back a step for a moment in my story, recently my Canems system had suffered a looping priming pulse issue which was clearly down to electromagnetic interference, typically such issues are the result of an earth loop on an electrical competent such as the fuel pump, radiator fans ect ect. Danny Lloyd kindly had a go at finding the issue and at no cost to myself which shows they stand by their product and look to provide good after sales support, however while he made the issue a bit better a few weeks later the dreaded looping returned with a vengeance, so like all the challenges in my life I decided to fix it myself.
I tested a number of components and discovered the problem was the idle air control valve, disconnecting it stopped the looping priming pulse instantly, and reconnecting it brought it back. So for a while I simply ran the car with the idle valve disconnected. Interestingly even with the valve electrically disconnected the damn thing is still bleeding air, but I did notice not only was the dreaded looping priming pulse issue now solved but the car actually drove smoother and the AFRs where more stable like this.
This reminded me once more of that statement those talented old mechanics I had the privilege to learn from some 25 years ago or more beat into me over and over again, IE...
"All vacuum leaks must be absolutely eliminated before you start the tuning process"
Clearly even though I'm running closed loop wide band lambda fueling and a sophisticated pulse width modulated rotary idle air control valve the Canems ECU had been struggling to manage it all to deliver the smoothest possible engine behavior, all this because just like a carb fed engine the fundamental rule for any internal combustion engine still very much applies even if it's on a far more sophisticated fuel injection system, IE ...
"When tuning any fuel system, all vacuum leaks are bad".
This got me thinking
What if I went back to what I was always taught, what if I returned to the teachings of those clever old mechanics who literally had the benefit of 50 years of engine tuning experience under their belt?
So having now fixed the annoying priming pulse issue myself and having seen some AFR stability and engine behavior benefits that came with disconnection the Bosch idle air control valve electrically, I set about going back to the fundamental lessons I was taught all those years ago. If all vacuum leaks are bad what if I not only disconnect the idle air control valve electrically, what if I completely remove it?. One of the other lessons I was taught all those years ago was that the ultimate induction system is a completely sealed one, that is the only air the engine is allowed to consume comes from one place only and that place being the throttle butterfly.
Going back to my early basic training I decided to implement the following arrangement:
1. I removed the problematic Bosch idle air control valve completely
2. I sealed the pipe that connects it to the back of the plenum
3. I removed the plenum, turned it upside down and removed the 3/32" alen headed grub screw that acts as the throttle stop
4. I inserted the 3/32" alen headed grub screw from the top so I could adjust the throttle stop easily from above and then replaced the plenum
5. Screwed the base idle screw right home to eliminate another vacuum leak
6. With the engine fully warm I set my idle speed using the 3/32" alen headed grub screw, IE on throttle butterfly rest position only
Basically I've gone back to how I was taught to set up a carb fed engine, this sounds a bit daft on a fuel injected system but reassured by the unshakable fact that the principles of any spark ignition internal combustion engine are the same irrespective of it's fuel delivery system I was confident what those very very experienced mechanics taught me all those years ago would still apply on on my Canems equipped TVR.
And boy oh boy was I right, my long time wandering AFRs immediately became super stable, the kind of rock solid figures I never dreamed possible... It then became immediately obvious to me why the MBE system from Powers Performance doesn't run an idle air control valve at all, my guess is whoever designed that system enjoyed the same fundamental old school engine tuning lessons I benefited from, IE...
" When tuning an internal combustion engine... ALL VACUUM LEAKS ARE BAD!"
I'm in no doubt far more sophisticated OEM engine management systems have the processing power and fast acting compensation strategies to run an idle air control valve effectively without causing issues.... or idle valves like the (copy) Bosch one used on the Canems system simply wouldn't exist. However, my experience with the Canems system is it just can't manage the idle valve accurately enough, or at least it's idle valve fuel correction feature just can't respond quickly or accurately enough to manage the infinitely variable rise and fall of air the valve is constantly bleeding into the engine.
Maybe there's wiring and earth issues at play on the Canems TVR installation too, perhaps the use of a non original pattern Bosh type idle valve by Lloyds doesn't help either, perhaps its both? I'd say it's these elements combined with that fundamental 'all vacuum leaks are bad' fact simply means the engine is so much happier with no idle valve fitted at all, just as Powers Performance do it with their MBE system.
Following my absolutely inarguable findings I will not be returning to using any form of idle air control valve ever again, I am now using 'Scatter Spark' to control my idle speed and aid cold starts as managing idle speed using ignition timing is infinitely better than the highly compromised air bleed method. As those with the MBE system will tell you the only minor downside is you need to keep the engine alive on the throttle pedal for the first 30 seconds of cold start, after that the ignition timing takes over to deliver a completely autonomous system that does not relay on what was effectively a poorly ECU managed vacuum leak.
Holding the throttle open manually for the first 30 seconds of cold starts seems mildly ridiculous, this is fuel injection after all so I really shouldn't need to do this, but the benefits of having no idle air control valve are so great it really is a tiny price to pay for the massive improvements in idle quality, fuel economy and drivability my sealed setup delivers. My final point would be that idle air control valves are actually very old hat technology these days, idle air control valves have long since been replaced with drive by wire throttle systems that effectively do what I need to do with my foot and throttle pedal for those first 30 seconds of cold start.
I see now the Lloyd Specialist Developments themselves are moving over to drive by wire throttle management, this makes a lot of sense to me as my experience with the Canems controlled idle air control valve has not been a good one for many reasons. For others running the Canems system my advice would be to get rid of their pattern part Bosch idle valve copy and follow my sealed system that you adjust the idle speed on throttle butterfly rest position and scatter spark only.
If my experiences are anything to go by... You will be absolutely delighted with the results..
"All vacuum leaks must be absolutely eliminated before you start the tuning process"
This rule applies to all spark ignition internal combustion engines, it's really irrelevant if it's fed by a carb or injection, it's fundamentally still very much just a spark ignition internal combustion engine, these old boys I worked with really were very insistent on this point and of course it makes perfect sense, so it's stayed with me all these years
Now consider this.... it doesn't matter if you're running a idle air circuit on a carb, a stepper motor as used on the 14CUX, or the supposedly far more sophisticated PWM controlled infinitely variable rotary Bosch Idle Air Control Valve as used on the Canems system, the truth is they are all really just vacuum leaks!
Now let me take you back a step for a moment in my story, recently my Canems system had suffered a looping priming pulse issue which was clearly down to electromagnetic interference, typically such issues are the result of an earth loop on an electrical competent such as the fuel pump, radiator fans ect ect. Danny Lloyd kindly had a go at finding the issue and at no cost to myself which shows they stand by their product and look to provide good after sales support, however while he made the issue a bit better a few weeks later the dreaded looping returned with a vengeance, so like all the challenges in my life I decided to fix it myself.
I tested a number of components and discovered the problem was the idle air control valve, disconnecting it stopped the looping priming pulse instantly, and reconnecting it brought it back. So for a while I simply ran the car with the idle valve disconnected. Interestingly even with the valve electrically disconnected the damn thing is still bleeding air, but I did notice not only was the dreaded looping priming pulse issue now solved but the car actually drove smoother and the AFRs where more stable like this.
This reminded me once more of that statement those talented old mechanics I had the privilege to learn from some 25 years ago or more beat into me over and over again, IE...
"All vacuum leaks must be absolutely eliminated before you start the tuning process"
Clearly even though I'm running closed loop wide band lambda fueling and a sophisticated pulse width modulated rotary idle air control valve the Canems ECU had been struggling to manage it all to deliver the smoothest possible engine behavior, all this because just like a carb fed engine the fundamental rule for any internal combustion engine still very much applies even if it's on a far more sophisticated fuel injection system, IE ...
"When tuning any fuel system, all vacuum leaks are bad".
This got me thinking
What if I went back to what I was always taught, what if I returned to the teachings of those clever old mechanics who literally had the benefit of 50 years of engine tuning experience under their belt?
So having now fixed the annoying priming pulse issue myself and having seen some AFR stability and engine behavior benefits that came with disconnection the Bosch idle air control valve electrically, I set about going back to the fundamental lessons I was taught all those years ago. If all vacuum leaks are bad what if I not only disconnect the idle air control valve electrically, what if I completely remove it?. One of the other lessons I was taught all those years ago was that the ultimate induction system is a completely sealed one, that is the only air the engine is allowed to consume comes from one place only and that place being the throttle butterfly.
Going back to my early basic training I decided to implement the following arrangement:
1. I removed the problematic Bosch idle air control valve completely
2. I sealed the pipe that connects it to the back of the plenum
3. I removed the plenum, turned it upside down and removed the 3/32" alen headed grub screw that acts as the throttle stop
4. I inserted the 3/32" alen headed grub screw from the top so I could adjust the throttle stop easily from above and then replaced the plenum
5. Screwed the base idle screw right home to eliminate another vacuum leak
6. With the engine fully warm I set my idle speed using the 3/32" alen headed grub screw, IE on throttle butterfly rest position only
Basically I've gone back to how I was taught to set up a carb fed engine, this sounds a bit daft on a fuel injected system but reassured by the unshakable fact that the principles of any spark ignition internal combustion engine are the same irrespective of it's fuel delivery system I was confident what those very very experienced mechanics taught me all those years ago would still apply on on my Canems equipped TVR.
And boy oh boy was I right, my long time wandering AFRs immediately became super stable, the kind of rock solid figures I never dreamed possible... It then became immediately obvious to me why the MBE system from Powers Performance doesn't run an idle air control valve at all, my guess is whoever designed that system enjoyed the same fundamental old school engine tuning lessons I benefited from, IE...
" When tuning an internal combustion engine... ALL VACUUM LEAKS ARE BAD!"
I'm in no doubt far more sophisticated OEM engine management systems have the processing power and fast acting compensation strategies to run an idle air control valve effectively without causing issues.... or idle valves like the (copy) Bosch one used on the Canems system simply wouldn't exist. However, my experience with the Canems system is it just can't manage the idle valve accurately enough, or at least it's idle valve fuel correction feature just can't respond quickly or accurately enough to manage the infinitely variable rise and fall of air the valve is constantly bleeding into the engine.
Maybe there's wiring and earth issues at play on the Canems TVR installation too, perhaps the use of a non original pattern Bosh type idle valve by Lloyds doesn't help either, perhaps its both? I'd say it's these elements combined with that fundamental 'all vacuum leaks are bad' fact simply means the engine is so much happier with no idle valve fitted at all, just as Powers Performance do it with their MBE system.
Following my absolutely inarguable findings I will not be returning to using any form of idle air control valve ever again, I am now using 'Scatter Spark' to control my idle speed and aid cold starts as managing idle speed using ignition timing is infinitely better than the highly compromised air bleed method. As those with the MBE system will tell you the only minor downside is you need to keep the engine alive on the throttle pedal for the first 30 seconds of cold start, after that the ignition timing takes over to deliver a completely autonomous system that does not relay on what was effectively a poorly ECU managed vacuum leak.
Holding the throttle open manually for the first 30 seconds of cold starts seems mildly ridiculous, this is fuel injection after all so I really shouldn't need to do this, but the benefits of having no idle air control valve are so great it really is a tiny price to pay for the massive improvements in idle quality, fuel economy and drivability my sealed setup delivers. My final point would be that idle air control valves are actually very old hat technology these days, idle air control valves have long since been replaced with drive by wire throttle systems that effectively do what I need to do with my foot and throttle pedal for those first 30 seconds of cold start.
I see now the Lloyd Specialist Developments themselves are moving over to drive by wire throttle management, this makes a lot of sense to me as my experience with the Canems controlled idle air control valve has not been a good one for many reasons. For others running the Canems system my advice would be to get rid of their pattern part Bosch idle valve copy and follow my sealed system that you adjust the idle speed on throttle butterfly rest position and scatter spark only.
If my experiences are anything to go by... You will be absolutely delighted with the results..
Edited by ChimpOnGas on Thursday 19th July 14:30
You're not just a pretty face Ian
This is how I've set things up....
1. I set the natural idle speed on the fully warmed engine high at 1,200rpm
2. The idle timing on my LPG ignition map is actually 21 degrees
3. Satter Spark only comes into play above 40 degrees, below this I get the jacked throttle possition plus 21 degrees
4. Once the engine is warm it would naturally race at 1,200rpm but of course with the coolant over 40 degrees scatter spark steps in and is now pulling timing to hit my 1,000rpm target
5. Like this while my ignition table shows 21 degress the engine is actually hapily idling away at 16 degrees
6. When the rad fans chime in I may see this number go up to 17 or 18 degrees but basically its always pulling timing from the 21 in my table
The idea is to run a bit more throttle opening than I actually need which helps during the warm up phase, then wnen the engine is fully warmed the ECU is only ever pulling 4,5 or 6 degrees of idle timing to hold the idle speed down to the 1,000rpm target.
This seems to work well, I only need to tickle the throttle by 2% for the first 30 seconds or less before the whole arrangement becomes completely autonomous and the engine idless perfectly all on it's own at 1,000rpm from there on. I know cold starts arent really cold starts in this weather as coolant temps seldome drop below 20 degrees even if the car has been sat for days on end, so there may be some fun to come when things cool off and we enter the Autumn months.
But I will find a solution, and I can absolutely guarantee you it will not involve an idle air control valve!
This is how I've set things up....
1. I set the natural idle speed on the fully warmed engine high at 1,200rpm
2. The idle timing on my LPG ignition map is actually 21 degrees
3. Satter Spark only comes into play above 40 degrees, below this I get the jacked throttle possition plus 21 degrees
4. Once the engine is warm it would naturally race at 1,200rpm but of course with the coolant over 40 degrees scatter spark steps in and is now pulling timing to hit my 1,000rpm target
5. Like this while my ignition table shows 21 degress the engine is actually hapily idling away at 16 degrees
6. When the rad fans chime in I may see this number go up to 17 or 18 degrees but basically its always pulling timing from the 21 in my table
The idea is to run a bit more throttle opening than I actually need which helps during the warm up phase, then wnen the engine is fully warmed the ECU is only ever pulling 4,5 or 6 degrees of idle timing to hold the idle speed down to the 1,000rpm target.
This seems to work well, I only need to tickle the throttle by 2% for the first 30 seconds or less before the whole arrangement becomes completely autonomous and the engine idless perfectly all on it's own at 1,000rpm from there on. I know cold starts arent really cold starts in this weather as coolant temps seldome drop below 20 degrees even if the car has been sat for days on end, so there may be some fun to come when things cool off and we enter the Autumn months.
But I will find a solution, and I can absolutely guarantee you it will not involve an idle air control valve!
Sardonicus said:
Dave a cranked open butterfly is an air leak even idle by-pass, a PCV valve is an air leak inc the standard RV8 system and yes the ICV is also another air leak (the later two un-metered because of fluctuation in reality) its why closed loop is available inc CL idle to compensate 
not always a perfect solution I'll grant you (we may not all use CL but mainstream manufacturers do) no production car I know of suffer from electrical noise because fitted with an ICV either rotary or stepper not knocking the Canems they can all have their foibles but I think you have another issue your masking by disconnection 
fixing the symptom rather than the actual problem , Alun sorry to hear your news fella 
this forum would definitely suffer without your input and good humour
Simon, the difference between running a fractionally too open throttle butterfly where the idle is held down with timing, and a Canems managed idle air control valve.... is stability! Sure, the Canems system has fuel correction for idle valve duty but I'm far from convinced it's fast or accurate enough to compensate for the variable air bleed introduced by the Canems managed pattern part Bosch idle air control valve. not always a perfect solution I'll grant you (we may not all use CL but mainstream manufacturers do) no production car I know of suffer from electrical noise because fitted with an ICV either rotary or stepper not knocking the Canems they can all have their foibles but I think you have another issue your masking by disconnection fixing the symptom rather than the actual problem , Alun sorry to hear your news fella this forum would definitely suffer without your input and good humour I'm also not convinced the software is showing me (or the ECU) true idle duty, unstable AFRs raised genuine suspicions that needed investigating properly.
Think about it Simon, even if it's been electrically disconnected that idle valve is still bleeding air all the time, not just at idle, and I'm sorry that in itself is not right!
With my throttle butterfly only setup, the idle valve gone, and the plenum sealed.... that nasty constant vacuum leak from the IACV is immediately eliminated. As you say, at idle the jacked throttle butterfly position is indeed bleeding air just like the idle valve would be....But as soon as you move off idle there's now no idle valve bleed anymore, like this 100% of the air the engine is allowed to consume comes entirely via the throttle butterfly, rather that X% from the throttle butterfly plus Y% from the constant air bleed from the idle valve!
The 100% air via the throttle butterfly setup is going to have little or no effect at idle, but as soon as you come off idle because all the air entering the engine is controlled directly by your foot the result is going to be better throttle response, this is fact because I've tested and felt it. In the standard idle valve setup some of the air is being controlled by your foot and some of it enters the engine outside of human control by a ECU controlled idle valve that could be doing anything for what good the duty figure is showing. The truth is irrespective of what the duty figure is telling you I can confirm the volume of air entering via the idle valve is actually rising and falling, basically and to a small degree you are actually no longer 100% in full control of the amount of air you are allowing into the engine, I can confirm this loss of driver control directly translates in your brain as a loss of throttle response and other undesirable engine behaviors.
With an errant ECU managed idle valve where the volume of air is increasing and decreasing outside of driver command, closed loop fueling is also now working far harder to smooth those errant spikes and dips in air to hit your closed loop AFR target. You've given over a % of air introduced into the engine to be controlled by the ECU and the pattern part Bosch idle valve it's managing.... so you better hope the ECU is doing a good job of this
Not content with guessing but driven by what I see and was taught, the way to prove or disprove my theoory was to not only disconnect the idle valve electrically which definitely solved to looping issue, but to remove the idle valve completely and seal the plenum it feeds. As stated the first thing that happened when I electrically disconnected my idle valve is the dreaded looping priming pulse disappears, you need to understand this looping has serious safety implications in my case. I say this because the fault is not only looping the priming pulse and pertrol pump, in my case its also looping the LPG safety solenoids. So if with the ignition on in position one before cranking you're looping the priming pulse (opening the injectors in a continuous loop), and at the same time you're loop opening your LPG safety solenoids you are are effectively running an open flow of LPG directly into the plenum.
I'll let you guess whats going to happen then, yes you guesses it you're pushing ever more gas into the plenum until you crank and start the engine. Quite an effective bomb really just waiting for a source of ignition to wake up your world, or fortunately as in my case, sufficient gas pressure to laterally pop the MaP hose off the back of the plenum to give a top of the map super rich fixed atmosphere signal and make the car virtually undrivable, a kind of safety system in itself if you want to look at it that way
So with the idle air control valve disconnected normal safe service is resumed and I can hand my ISIS membership card back which feels good to be honest, but hey, look at that, the AFRs are more stable too. So maybe I was right all along, maybe that steady duty displayed on my laptop was actually (as I suspected all along) was actually going up and down like a haw's draws, well it certainly seems that way to me
The second thing that happened with the plenum now sealed and the valve no longer bleeding air is my AFRs became even more stable still, so I go for a drive, and boy she's smoother. Throttle response is improved too and after some extensive testing I also gained an 8% improvement in fuel economy, quite simply with the idle valve removed the car is better better better in many many ways.
So this got me thinking, how much does my engine actually need this fancy schmancy ECU managed PWM idle air control valve anyway, I cant help thinking back to the beautiful rock solid idles I achieved when tuning simple carb fed engines and none of them had or needed all this sophisticated processor managed air bleed idle business
. So as it turns out the answer to that question is my old gas powered Rover V8 hardly needs any help to idle at all, excluding the first 30 seconds of cold start where she needs an addition foot activated 3% throttle opening my engine idles rock solid just like all those basic carb engines I used to tune.So the the reality is my engine only needs a fancy schmancy ECU managed PWM idle air control valve for less that 0.0001% of its operating time, after that all my Canems idle valve was merely producing a safety issue and running problems, can you see now why I'm not a fan Simon?
The irony of all this is the Canems system is designed to work with the Bosch idle valve but seems entirely incomparable with it in my case, the very idle valve the ECU is meant to work with was causing the priming pulse, my petrol pump, and more worryingly my LPG safety solenoids to loop. More than this the ECU was instructing the valve to let rising and falling amounts of air into the engine outside of that the calibration was telling it too, to add to it all this wasn't immediately obvious as the duty figures weren't displaying the true valve behavior.
This post isnt a dig at anyone, least of all Lloyd Specialist Development or Canems, it's a series of factual observations and a concluded summary of the genuine results of my tests and findings. The Canems Dual Fuel System has always delivered astonishing efficiency, drivability and fuel economy results compared with my old distributor and 14CUX system, it's just now with the idle valve removed it's even better still.
carsy said:
I can see how in closed loop idle with your valve constantly altering and then the fueling trying to catch up how things can become a little iratic shall we say. But surely as soon az you touch the throttle it will jump out of idle mode and therefore the idle valve SHOULD stay at a fixed position until you fall back into idle mode again.
Yes Ian, this is how it SHOULD work, there are lots of settings to manage the idle valve in the Canems software.
Some people (not you Ian) always seem super keen to jump on the negative, especially if the discussion centres around a competetor's product. The truth is the Canems system has absolutely transformed my TVR, it drives immeasurably better and the car performs stronger than when it was new. Best of all it delivers a petrol fuel consumption figure of 51mpg which is totally game changing when a 300 mile fill of petrol these days is over £70, to cover the same distance in 'Ol Gas Bag' is a massively more pocket friendly £33.
Saying that the system really shouldn't loop the priming pulse and the other '2 second on' elements especially my LPG safety solenoids, this could be a wiring loom fault, and earthing issue, an ECU fault, or maybe the system just needs to be paired with a genuine £100 Bosch idle valve not a £40 copy? But that aside I've noticed that even with the thing disconnected electrically the valve is still flowing a lot of air so no one can convince me it's anything other than a huge vacuum leak. When I worked in restoration all those years ago if I'd tried to tune an engine like that, the experienced mechanics I worked under would have given me a proper clip round the ear. Of course you can just add fuel to compensate for all that air, the Canems system makes that easy, but that's not the right way to approach the situation, the way to tackle a big vacuum leak is to eliminate the big vacuum leak in the first place, then start the tuning process!
By removing the constantly air bleeding idle valve and sealing the plenum where it supplies all that air, a massive vacuum leak is eliminated. Like this the engine is definitely smoother, AFRs more stable and generally it's much much easier to map, this should surprise no one with a basic understanding of engine tuning. I was trained and cut my teeth on tuning carb fed engines but the rules are exactly the same, there's no way on Gods earth you're going to achieve good results with the kind of massive vacuum leak that idle valve was inflicting on my engine
Worse still even though closed loop idle is only active under 2% TPS and does nothing until 83 degrees coolant, I'm not convinced the idle valve really was holding the fixed duty the software said it was at idle, forget the on screen duty figure going old school and testing the theory with a vacuum gauge proved my point. I really didn't need to do this to prove the point as the fluctuating MaP signal was displaying the exact same results, after all the MaP sensor and ECU is really just a permanently plumbed in vacuum gauge.
So with the constantly air bleeding idle air control valve now gone and it's feed to the plenum sealed... it really didn't surprise me to see my MaP signal became massively more stable!
Sardonicus said:
Have you re-calibrated your TPS in the Canems software now Dave? seeing as you have changed the idle/throttle angle, your car probably thinks its permanently on part throttle never reaching the idle position well it would do if you was using MS for example just a heads up 
Yes, of course Simon, it takes seconds with the Canems system, it's super easy. just a heads up I must have done well over 1,000 miles in the last two weeks since deleting the Idle valve and there are only benefits, ironically excluding the first 30 seconds of cold start the engine really doesn't need the IACV at all.
A clear case of an unnecessary complication causing more issues that it solves.
Mr2Mike said:
The last part of your post is simply incorrect. An IACV allows metered air into the engine in order to control idle speed. The vacuum leaks your elders taught you to eliminate are all concerned with unmetered air, which will cause weak mixtures, inconsistent idle speed etc.
Sorry, but the valve is open all the time, it is therefore a permanent open to atmosphere vacuum leak and is no different to any there vacuum leak, you can add fuel to compensate but this is masking not curing.Unsurprisingly with the idle valve removed and the path of errant air sealed the MaP signal is more stable, throttle response is improved, idle is more stable and generally drivability at small throttle openings is greatly improved too.
Anything that isn't the throttle butterfly is a vacuum leak, because the throttle butterfly is the device the driver uses to regulate how much air the engine is permitted to receive, indeed the truth is even the crankcase ventilation system is a vacuum leak, just a necessary one but only really for environmental reasons. Back in the day cars ran draught tubes, effectively a pipe that connected the crankcase directly to atmosphere, it basically puked oil and crankcase gasses directly onto the road.
All vacuum leaks are bad which is why my TVR engine behaves better without that permanently open idle valve, fact!
Mr2Mike said:
This shows a fundamental lack of understanding. If the car uses a mass air sensor, the air for the IACV will be drawn through the sensor, and therefore metered. If the car uses a MAP sensor, then the air flowing through the IACV will lower manifold vacuum, and will therefore be metered.
Using your own definition, the throttle is also a vacuum leak which can be compensated by adding fuel. This is therefore masking exactly the same "fault" that you accuse an IACV of causing.
Using your own definition, the throttle is also a vacuum leak which can be compensated by adding fuel. This is therefore masking exactly the same "fault" that you accuse an IACV of causing.
Correct, the throttle butterfly is indeed a vacuum leak, it's just the very one you use to control how much air the engine receives and so is the method used to regulate engine speed. An internal combustion engine is just a big vacuum pump, if you stop it drawing any air at all it the engine would simply stop, it needs to get air from somewhere so this is why we have a throttle butterfly.
You've chosen to call me on metered air when I'm not even talking about metered air, this shows a fundamental lack of understanding of this post
. There are two types of air that enter an engine:
1. Controlled Air - Any air that enters the engine controlled directly by the driver
2. Uncontrolled Air - Any air that enters the engine that is not directly controlled by the driver
The important thing to understand here is in my case where a MaP sensor is used both controlled air and uncontrolled air will always be metered because the MaP sensor is merely measuring the depression (the vacuum) in my plenum, I could cut my servo pipe in half and all that extra air would still be metered by my MaP sensor and ECU.... but that doesn't make it good now does it?
Actually there are two types of uncontrolled air, Intentional and Unintentional.
Examples of intentional uncontrolled air on our cars include the carbon canister purge valve, the crankcase ventilation system, and the stepper motor. Remember controlled air can only come from direct driver input, air entering via the purge valve or stepper motor may indeed be ECU managed but it still falls into the category of uncontrolled because the driver is not directly controlling it himself.
In an ideal world all the air the engine receives should come solely from the throttle butterfly and therefore be 100% Controlled Air, this is because the throttle butterfly is the one and only valve the driver controls with his foot to directly regulate engine speed. If you have an idle valve that remains partially open all the time rest assured it most definitely is uncontrolled air, indeed I would argue it isn't even intentional uncontrolled air. A partially and permanently open idle valve is introducing uncontrolled air to the engine or in other words is just another vacuum leak, yes the MaP sensor will give you a figure that includes it, but it's still a vacuum leak all the same!
Any air that enters the engine outside of that controlled by the driver will effect how crisp the throttle response feels especially as you pull away off idle, eliminating any source uncontrolled air will therefor always enhance throttle response. Unfortunately you will never eliminate it all as some uncontrolled air like that introduced by the crankcase breather system is essential for environmental reasons, however, uncontrolled air the from the always open idle valve is something you can and should address
That split second as you crack the throttle open and pull away is more important than you think, it has a big impact on what we call throttle response, improving this aspect also has a big impact on how easy the car is to control at slow speeds like reverse parking and generally when you're maneuvering at walking pace. If you eliminate the uncontrolled air (the vacuum leak) inflicted on the engine by a partially and permanently open IACV, no longer is the engine receiving 80% controlled air from the throttle butterfly, 15% uncontrolled air coming from the always open idle valve, and 5% from the crankcase ventilation system. With the idle valve removed and the feed pipe sealed 95% of the air now entering the engine is driver controlled air from the throttle butterfly with the small addition of the 5% from the crankcase ventilation system.
Like this each mm of throttle pedal movement made far more directly translates to a change in engine speed as instructed solely by the driver himself, this is the very definition of control, and another term for that control is throttle response. In addition to this the driver will find the car far more controllable during low speed maneuvering, with idle speed now set on throttle butterfly gap only you'll find you can simply lift the clutch with no throttle input at all to complete your low speed maneuvers without risking a stall. Idle speed is the same as it was when the always open IACV contributed 15% of the air needed to achieve that idle speed, but all of a sudden you've lost that nasty fluffy spot that meant you needed to excessively rev the engine or slip the clutch when parking, it's quite surprising just how much this small improvement alone contributes to a nicer calmer driving TVR.
If it doesn't matter that the idle valve is a permanently open to atmosphere vacuum leak that bypasses the throttle butterfly, why is it so important to make sure we don't have other vacuum leaks like a split servo hose or PCV hoses ect ect? If it didn't matter the idle valve is always open why are are we always taught to chase down all vacuum leaks on an engine before starting the tuning process? Is the big old vacuum leak passing down the permanently open idle valve in some way special uncontrolled air that's somehow good for engine behavior and breaks all the rules of engine tuning? No, of course it's not, its just another big old uncontrolled vacuum leak like any other, and one that needs eliminating.
Metered uncontrolled air from a vacuum leak doesn't make it good air just because you're metering it, what you should be doing is eliminating that nasty vacuum leak in the first place, that way you're no longer fighting to compensate for it!
The thing I don't like about my Canems idle valve is it always remains open to atmosphere even when it's not needed, and I only really noticed this recently, it's not like it's a small vacuum leak either, it flows a lot of air! My second observation after experimenting with it removed... is just how little the engine actually needs the valve anyway! So in my case the IACV is a big old permanent vacuum leak being generated by a device that 99.9% of the time simply isn't needed.
That's hardly a strong argument to keep the damn thing now is it, quite the opposite in fact!
The looping priming pulse issue is a different matter, that was not only a frustrating issue but a potentially dangerous one too, others spent some considerable time at their own cost trying to fix it but the truth is I still found the only way to solve the problem was to disconnect it's electrical connector. As soon as I pulled the plug on the IACV the looping priming pulse disappeared, reconnect it and the dreaded looping returned
Anyway back to the fact the valve is always open to atmosphere even when it's not needed, surely that's not right? My tests prove all my engine needs an IACV for is to raise the idle speed on cold start by the equivalent of the air introduced by a 3% manually opened throttle butterfly and even then it only needs that extra air for 30 second or so as the engine warms.
After the 30 second warm up phase the engine needs no additional air (or even scatter spark really) to maintain a lovely fixed solid 1,000rpm idle all day long, and even on a restart after the car has been left for a few hours. Based on this observation personally I would be designing a permanently closed idle valve that only opens on cold start, as soon as the first 30 seconds of cold start has passed it would return to it's natural fully closed position because quite simply it's no longer needed or indeed beneficial to have it leaking away as it does.
So if someone can tell me why my IACV stays open always I'd love to know, the engine is most definitely happier without the permanent vacuum leak it creates and as proved the engine doesn't even need the idle valve for 99.9% of the time anyway. To me it's a fault, it should never be sat there just unnecessarily bleeding air like it is all day
These are just my observations based on fact and testing the car either way, I know a happy engine when I hear one and my engine is way happier with 'Hissing Sid' the leaky IVAC is sat on my bench. My guess is not even the Lucas stepper motor creates such a monumental vacuum leak as my Canems controlled Bosch idle valve did, no matter what I did with the settings it was always sat roughly at 40% duty which is one hell of a lot of extra air to throw at an idling engine that doesn't even need it.
To me the permanently open idle valve is little or no different to drilling a big hole in my plenum and just leaving it open to atmosphere all the time, and you wouldn't do that out of choice now would you? I appreciate my learning is old school, but a big vacuum leak like that is never a good thing, so surely an idle valve that constantly sits there 40% open to atmosphere can't be right or good for engine behavior
That's hardly a strong argument to keep the damn thing now is it, quite the opposite in fact!
The looping priming pulse issue is a different matter, that was not only a frustrating issue but a potentially dangerous one too, others spent some considerable time at their own cost trying to fix it but the truth is I still found the only way to solve the problem was to disconnect it's electrical connector. As soon as I pulled the plug on the IACV the looping priming pulse disappeared, reconnect it and the dreaded looping returned
Anyway back to the fact the valve is always open to atmosphere even when it's not needed, surely that's not right? My tests prove all my engine needs an IACV for is to raise the idle speed on cold start by the equivalent of the air introduced by a 3% manually opened throttle butterfly and even then it only needs that extra air for 30 second or so as the engine warms.
After the 30 second warm up phase the engine needs no additional air (or even scatter spark really) to maintain a lovely fixed solid 1,000rpm idle all day long, and even on a restart after the car has been left for a few hours. Based on this observation personally I would be designing a permanently closed idle valve that only opens on cold start, as soon as the first 30 seconds of cold start has passed it would return to it's natural fully closed position because quite simply it's no longer needed or indeed beneficial to have it leaking away as it does.
So if someone can tell me why my IACV stays open always I'd love to know, the engine is most definitely happier without the permanent vacuum leak it creates and as proved the engine doesn't even need the idle valve for 99.9% of the time anyway. To me it's a fault, it should never be sat there just unnecessarily bleeding air like it is all day
These are just my observations based on fact and testing the car either way, I know a happy engine when I hear one and my engine is way happier with 'Hissing Sid' the leaky IVAC is sat on my bench
. My guess is not even the Lucas stepper motor creates such a monumental vacuum leak as my Canems controlled Bosch idle valve did, no matter what I did with the settings it was always sat roughly at 40% duty which is one hell of a lot of extra air to throw at an idling engine that doesn't even need it.To me the permanently open idle valve is little or no different to drilling a big hole in my plenum and just leaving it open to atmosphere all the time, and you wouldn't do that out of choice now would you? I appreciate my learning is old school, but a big vacuum leak like that is never a good thing, so surely an idle valve that constantly sits there 40% open to atmosphere can't be right or good for engine behavior
Many thanks for the above spitfire4v8,
There's some really excellent and helpful information in your post so a genuine thank you from me for sharing your knowledge.
TBH the looping issue was disappointing and only presented itself when I fitted my latest replacement ECU from David Hampshire which apparently came with a revision to the crank position sensor circuit, David Hampshire explained this was an improvement but in my case it came with the new and never before experienced looping issue so it was hard for me to agree. While I do not want to expose the full history on these pages it would seem as an early Canems adopter and serial advocate my reward has been I took on some development frustrations that have followed me throughout the last five years.
Certainly, and especially in more recent times, it became clear my earlier Canems loom wasn't entirely comparable with the latest replacement Mk4 ECU kindly sent to me by David Hampshire, however I was surprised that Mr Hampshire advised me to bare the shielding of the crank signal wire and earth it directly to the battery. I think he was just trying to be helpful as the battery is close to ECU in a Chimaera but it has always been by understanding all sensors should be 'Start Earthed' to one common point, which is preferably a stout bolt on the engine block, or the N/S cylinder head in the case of a Chimaera.
While earthing the shielding to the battery resolved the no-start condition I initially experienced with my Mk4 Dual Fuel ECU it also came with the looping priming pulse issue that ordinarily I might consider a frustration I could live with, but in the case of my Dual Fuel system the fault was also looping my LPG solenoids which was clearly a safety issue that urgently needed resolving. It was suggested to me this would involve a cost of £500 to resolve, but following some unsupported suggestions that I had in some way brought this issue on myself the team at Lloyd Specialist Developments did finally agree to correct the situation at no cost by earthing the the crank wire shielding correctly to the engine, unfortunately the fault while initially improved did very quickly return.
While there is an open offer to take the car back yet again, there comes a point where I need to just get on with enjoying my TVR, obviously I chose to change engine management system to improve reliability, drivability and fuel economy and the Canems system has certainly achieved two of those objectives, and of late while it's early days on my my Mk4 ECU it does seem to be demonstrating it can hit all three. Back to the subject of the idle valve and ignoring the looping priming pulse fault, I have my suspicions the Canems system in my case was failing to make a proper job of controlling the pattern part Bosch idle air control valve, the evidence is this issue is not unique to me or my Dual Fuel system either as I have also seen another Canems petrol only installation on a Chimaera where the solution to an over active IACV was to insert a crudely made hose restricting sleeve in the hose to the plenum which I could only describe as a bodge.
I have no idea if the issue is the choice to save costs by using a pattern part Bosch IACV copy rather than a genuine Bosch unit which may generate EMI and other issues due to poor shielding, or I guess it could also be an earthing issue or something inherently wrong with the loom? In a way I'm so over worrying about why, because the car now drives immeasurably better without the IACV and indeed it has proved to me that 99.9% of the time it genuinely doesn't even need the thing anyway!
However, like you say in an ideal world the system would work properly with the IACV in place, in an ideal world there would be no looping and the valve would be completely closed (or very nearly closed) 99.9% of the time, sadly this is just not the case for me and others so the valve stays on my bench where it can no longer give issues.
There's a lot of good information in your post regarding idle air control valves but I was especially interested to read this as it makes a lot of sense to me....
I absolutely love my TVR and that means I drive it a lot, it is a hobby car though and one that tends to cost me £1,000 a year in TAX, Insurance, MoT ect ect before it's even turned a wheel so that's £83 an month just for the privilege of having it sat in my garage doing nothing. I dont know about anyone else but I don't spend £83 a month for nothing on anything in my life, so my TVR needs to earn its keep. That means as an absolute minimum 'Ol Gasbag' needs to be serving me up £83 of pleasure every month or the thing is simply a money bleeding parasite, the pleasure for me is not constantly taking the car back to have things corrected, faults that shouldn't have existing in the first place, and I'm beggered if I'm going to keep shelling out money to resolve these issues that most certainly are not of my own making either!
The fix in this latest case was easy, just remove the damn idle valve, the car was off the road for 30 minutes and not 30 days as before and the results are immeasurably better and more successful. Yes it's disappointing I needed to do this, but if it's the difference between a safe and better driving TVR I can use and enjoy where the only down side is I need to hold the throttle open for the first 30 seconds of cold start.... then so be it. We are having the best summer in living memory, my TVRs roof hasn't been up in weeks and I've literally covered thousands of super happy reliable and lovely smooth driving miles in the car in the last month or so alone, this is what TVR ownership should be about not shipping the car back and forth to a specialist to see it returned with the same issue it went in with.
I hope this makes sense to people, it's not an attack on anyone but merely a statement of fact regarding my frustrations, I absolutely do not feel my position or truthful comments are unreasonable in any way, especially as I make them as a customer. I've tuned hundreds of carb fed engines in the past, this was my formal training, and in nearly all cases adding a dash of fast idle during the warm up phase couldn't be simpler. My TVR also needs a dash of fast idle but just like those carb fed engines, but just like those old carb fed engines I've also proved it absolutely only needs that dash of fast idle for the first 30 seconds of cold start. None of the carb engines I've tuned ever resorted to a sophisticated PWM rotary idle air control valve to achieve this, which in my mind does beg a very obvious question.
One final interesting points of note relates to cold start enrichment, with the idle valve connected a considerable additional requirement for fuel was most definitely needed, but with the IACV removed all that extra fuel quite clearly isn't required. I've proved this, during cold starts my IACV has been bleeding a huge amount of air and with all that air must come extra fuel, take away the air and the requirement for all that fuel disappears in a stroke. Cold starts are now sharp and instantaneous, and while I do need to hold the throttle butterfly open at 3% to save a stall for the first 30 seconds it most certainly doesn't need (or want) the huge amounts of fuel it did before.
In summary and in my case the benefits of running no idle valve are significant and many, so holding the throttle open for 30 seconds literally becomes what I would describe as an 'irrelevant minute inconvenience'. The bottom line is the engine only ever needs extra air for the first 30 seconds of cold start and to the value of what flows through a throttle butterfly that is only cracked open by 3%, as shown to us by the people who designed many different carburetors through the ages there are innumerable very simple and highly effective ways to achieve this without resorting to a sophisticated ECU managed PWM idle air control valve that in my case is clearly more trouble than it's worth.
Yes I could call on David Hampshire to get a stepper motor control written into the ECU but I don't think anyone would argue with me when I say David isn't always the fastest to respond, and the message will probably be the Bosch IACV system works fine anyway. Well it doesn't on my car, so please don't blame me for returning to my carb training to look at a far simpler and proven solution to adding a tiny bit more air for just 30 seconds of cold start, because quite simply that's all the engine needs!
Thanks again for sharing your knowledge
There's some really excellent and helpful information in your post so a genuine thank you from me for sharing your knowledge.
TBH the looping issue was disappointing and only presented itself when I fitted my latest replacement ECU from David Hampshire which apparently came with a revision to the crank position sensor circuit, David Hampshire explained this was an improvement but in my case it came with the new and never before experienced looping issue so it was hard for me to agree. While I do not want to expose the full history on these pages it would seem as an early Canems adopter and serial advocate my reward has been I took on some development frustrations that have followed me throughout the last five years.
Certainly, and especially in more recent times, it became clear my earlier Canems loom wasn't entirely comparable with the latest replacement Mk4 ECU kindly sent to me by David Hampshire, however I was surprised that Mr Hampshire advised me to bare the shielding of the crank signal wire and earth it directly to the battery. I think he was just trying to be helpful as the battery is close to ECU in a Chimaera but it has always been by understanding all sensors should be 'Start Earthed' to one common point, which is preferably a stout bolt on the engine block, or the N/S cylinder head in the case of a Chimaera.
While earthing the shielding to the battery resolved the no-start condition I initially experienced with my Mk4 Dual Fuel ECU it also came with the looping priming pulse issue that ordinarily I might consider a frustration I could live with, but in the case of my Dual Fuel system the fault was also looping my LPG solenoids which was clearly a safety issue that urgently needed resolving. It was suggested to me this would involve a cost of £500 to resolve, but following some unsupported suggestions that I had in some way brought this issue on myself the team at Lloyd Specialist Developments did finally agree to correct the situation at no cost by earthing the the crank wire shielding correctly to the engine, unfortunately the fault while initially improved did very quickly return.
While there is an open offer to take the car back yet again, there comes a point where I need to just get on with enjoying my TVR, obviously I chose to change engine management system to improve reliability, drivability and fuel economy and the Canems system has certainly achieved two of those objectives, and of late while it's early days on my my Mk4 ECU it does seem to be demonstrating it can hit all three. Back to the subject of the idle valve and ignoring the looping priming pulse fault, I have my suspicions the Canems system in my case was failing to make a proper job of controlling the pattern part Bosch idle air control valve, the evidence is this issue is not unique to me or my Dual Fuel system either as I have also seen another Canems petrol only installation on a Chimaera where the solution to an over active IACV was to insert a crudely made hose restricting sleeve in the hose to the plenum which I could only describe as a bodge.
I have no idea if the issue is the choice to save costs by using a pattern part Bosch IACV copy rather than a genuine Bosch unit which may generate EMI and other issues due to poor shielding, or I guess it could also be an earthing issue or something inherently wrong with the loom? In a way I'm so over worrying about why, because the car now drives immeasurably better without the IACV and indeed it has proved to me that 99.9% of the time it genuinely doesn't even need the thing anyway!
However, like you say in an ideal world the system would work properly with the IACV in place, in an ideal world there would be no looping and the valve would be completely closed (or very nearly closed) 99.9% of the time, sadly this is just not the case for me and others so the valve stays on my bench where it can no longer give issues.
There's a lot of good information in your post regarding idle air control valves but I was especially interested to read this as it makes a lot of sense to me....
spitfire4v8 said:
Another issue I have with the rotating valves is that they (possibly) are affected by pressure changes, such that on high vacuum the valve *might* be pulled more than the pwm signal would have you believe. I don't know this for sure, but it seems possible from the way they operate. It's not a big issue on AFM or MAP sensed cars as the airflow is sensed and fuel corrected accordingly, but cars mapped alpha-n with no manifold compensations might see changes in airflow which aren't accounted for, because the ecu doesn't know the valve has moved under vacuum from its intended position. It's one of the reasons I much prefer the more positive action of a stepper motor, the rack/plunger of which is largely unaffected by anything other than the signal operating it. As you have rightly pointed out in the past though, keep its action to the minimum required to get the job done. All my stepper motor valves are fully closed at normal operating temp, and because of the way the plunger system works there's no bleed-past.
There's a lot that rings true to me in the above, in fact there's a lot that makes a great deal of sense to me in your entire post so thank you once again for sharing your knowledge.I absolutely love my TVR and that means I drive it a lot, it is a hobby car though and one that tends to cost me £1,000 a year in TAX, Insurance, MoT ect ect before it's even turned a wheel so that's £83 an month just for the privilege of having it sat in my garage doing nothing. I dont know about anyone else but I don't spend £83 a month for nothing on anything in my life, so my TVR needs to earn its keep. That means as an absolute minimum 'Ol Gasbag' needs to be serving me up £83 of pleasure every month or the thing is simply a money bleeding parasite, the pleasure for me is not constantly taking the car back to have things corrected, faults that shouldn't have existing in the first place, and I'm beggered if I'm going to keep shelling out money to resolve these issues that most certainly are not of my own making either!
The fix in this latest case was easy, just remove the damn idle valve, the car was off the road for 30 minutes and not 30 days as before and the results are immeasurably better and more successful. Yes it's disappointing I needed to do this, but if it's the difference between a safe and better driving TVR I can use and enjoy where the only down side is I need to hold the throttle open for the first 30 seconds of cold start.... then so be it. We are having the best summer in living memory, my TVRs roof hasn't been up in weeks and I've literally covered thousands of super happy reliable and lovely smooth driving miles in the car in the last month or so alone, this is what TVR ownership should be about not shipping the car back and forth to a specialist to see it returned with the same issue it went in with.
I hope this makes sense to people, it's not an attack on anyone but merely a statement of fact regarding my frustrations, I absolutely do not feel my position or truthful comments are unreasonable in any way, especially as I make them as a customer. I've tuned hundreds of carb fed engines in the past, this was my formal training, and in nearly all cases adding a dash of fast idle during the warm up phase couldn't be simpler. My TVR also needs a dash of fast idle but just like those carb fed engines, but just like those old carb fed engines I've also proved it absolutely only needs that dash of fast idle for the first 30 seconds of cold start. None of the carb engines I've tuned ever resorted to a sophisticated PWM rotary idle air control valve to achieve this, which in my mind does beg a very obvious question
.One final interesting points of note relates to cold start enrichment, with the idle valve connected a considerable additional requirement for fuel was most definitely needed, but with the IACV removed all that extra fuel quite clearly isn't required. I've proved this, during cold starts my IACV has been bleeding a huge amount of air and with all that air must come extra fuel, take away the air and the requirement for all that fuel disappears in a stroke. Cold starts are now sharp and instantaneous, and while I do need to hold the throttle butterfly open at 3% to save a stall for the first 30 seconds it most certainly doesn't need (or want) the huge amounts of fuel it did before.
In summary and in my case the benefits of running no idle valve are significant and many, so holding the throttle open for 30 seconds literally becomes what I would describe as an 'irrelevant minute inconvenience'. The bottom line is the engine only ever needs extra air for the first 30 seconds of cold start and to the value of what flows through a throttle butterfly that is only cracked open by 3%, as shown to us by the people who designed many different carburetors through the ages there are innumerable very simple and highly effective ways to achieve this without resorting to a sophisticated ECU managed PWM idle air control valve that in my case is clearly more trouble than it's worth.
Yes I could call on David Hampshire to get a stepper motor control written into the ECU but I don't think anyone would argue with me when I say David isn't always the fastest to respond, and the message will probably be the Bosch IACV system works fine anyway. Well it doesn't on my car, so please don't blame me for returning to my carb training to look at a far simpler and proven solution to adding a tiny bit more air for just 30 seconds of cold start, because quite simply that's all the engine needs!
Thanks again for sharing your knowledge
Sardonicus said:
Dave I deleted my earlier post because I felt this thread was going round and round in circles and although I dont agree with some of your comments previously you posting this latest piece makes sense now and explains lots 
you have done what you needed to have your car functioning and so long as your happy thats good enough 
hope you make even more progress with the revised ECU onwards and upwards , I do feel that Canems should be supporting you with this however
There's a reason for everyting I do Simon, thanks as always for your support mate you have done what you needed to have your car functioning and so long as your happy thats good enough hope you make even more progress with the revised ECU onwards and upwards , I do feel that Canems should be supporting you with this however Edited by Sardonicus on Tuesday 24th July 14:07
spitfire4v8 said:
Good post, in the light of your frustrations it becomes clear why you've opted to run without the valve
As an aside, is your crank sensor inductive or hall effect? As you know a hall effect trigger is less susceptible to interference.
The canems supplies the prime though at key-on even before the engine turns? so if the looping was constant then that suggests a resetting of the ecu, thinking it's always in a repeating key-on situation. Anyway just idle musings
3 of my fleet are still on carbs, so I'm still keeping my hand in even in 2018
Thanks again Jools, the sensor used may answer your questions...As an aside, is your crank sensor inductive or hall effect? As you know a hall effect trigger is less susceptible to interference.
The canems supplies the prime though at key-on even before the engine turns? so if the looping was constant then that suggests a resetting of the ecu, thinking it's always in a repeating key-on situation. Anyway just idle musings
3 of my fleet are still on carbs, so I'm still keeping my hand in even in 2018
Its your typical variable reluctor type crank (or cam angle) sensor used with a toothed trigger wheel, as I'm sure you know they have a standard 2 pin mini timer socket, I believe its a Bosch - 0261 210 151 C?
It's my understanding these sensors were commonly used on work-a-day mid 90's Vauxhalls like Astras and the like, I couldn’t tell you if it's a genuine Bosch one but I do know for a fact my idle valve is a pattern part of unknown origin, so one must assume the same for the crank sensor. The funny thing is the IACV worked just fine on my two (or was it three?) Mk1 ECUs, my two Mk2 ECUs, and my Mk3 Canems ECU... I'm not sure I've got the numbers of ECUs right actually as I've had a few so it's easy to lose track.
Anyway, the looping fault only presented itself on my latest Mk4 ECU, let's call it ECU number four... or is it number five
. Oh hell I can't remember and the numbers arent so relevant, anway as a rule and on average they last about 9 months so after five years of all this it's easy to lose track. As we know God loves a trier and being a development engineer isn't alays an easy road, but I'm pretty sure we've got it right now, well as right as running no idle valve can be, I believe its safe now too which is always a bonus.The car definitely thanked me for removing the IACV, I immediately lost the looping issue, gained drivability, and I even picked up 8-10% fuel economy into the bargain. There isn’t a sum of money in the world that would encourage me to reinstate the thing so it sits on my bench as a permanent reminder that sometimes you're just better off fixing your own troubles in life.
This episode has also taught me to be tolerant of being falsely accused of brining troubles on myself, and the importance of keeping emails that run back some five years and the evidence they provide. We are at the 'It Just Needs to Work' point in all this but I guess you could argue it doesn’t if you include the looping issue with an idle valve fitted.
I'd like to thank David Hampshire and Lloyds Specialist developments for all the support they've given me and their offer to once again take the car back to correct the dreaded looping priming pulse fault, an offer I would like to hold in reserve as I understandably just want to enjoy my TVR is all this lovely weather we're having right now. With a Mk4 ECU housing what appear to be injector drivers that so far and after one whole year have yet to blown themselves apart, and the idle valve removed.... I'm just looking forward to a sustained period of reliability to go with the fantastic drivability and outstanding economy the Canems Dual Fuel ECU is delivering.
Thanks for listening and contributing folks, especially Jools & Simon who have stuck with me through my rather cryptic ways, my message is sent and so my work is done
Matthew Poxon said:
I would be tempted to chuck this back at either Lloyds or Canems to resolve, sounds like something is not right.
After the car had been with Lloyds for a few weeks and the car returned to me as fixed the looping returned withing days, so I spoke with Danny Lloyd and he immediately said he'd take the car back to look at it again, obviously it was disappointing the fault wasn't fixed in the first place but I have no issue with the support offered by Lloyds. The team at Lloyds are honest decent guys who just want to solve the problem and in many ways both I the customer and Lloyds themselves are victims of David Hampshires decision to send me a replacement ECU that had the new crank position sensor circuitry, a setup that apparently is incompatible with my earlier Canems loom. Saying that I only needed to approach David for help following yet another ECU failure, and Lloyds did recently have the car for a few weeks to sort out the looping that came with my latest replacement ECU.The thing is my TVR is for enjoying, I'm not losing another three weeks with the car right in the middle of the summer, so I've elected to take a rain check on sending it back once again, well for the time being at least. It's not like Warminster is just up the road for me either so multiple delivery and collections of the car becomes a royal PITA that sucks up my weekends or means I need to take time off work, ultimately it always seems to costs me money in fuel or train tickets, usually find myself begging a favor from a friend to run me down to collect the car.... and I'm running out of favors fast!
With all the above in mind I decided to look at the problem myself, within 30 minutes I'd worked out if I disconnected the idle valve the looping problem disappeared, reconnect it and it was back, I could literally turn the fault off and on at will simply by disconnecting and reconnecting the IACV.
The solution was simple..... disconnect the damn thing!
This lead me to experimenting with completely removing the IACV and sealing the plenum feed pipe it supplies, I figured if I was going to disconnect it electrically I may as well remove it completely. What I wasn't prepared for was all the benefits that came with removing the thing and sealing the plenum, the car drove better and idled smoother which was supported by a far more stable MaP signal, I also picked up an 8-10% improvement in fuel economy.
The biggest surprises though were.... firstly just how much fuel I needed to pull out of my cold start enrichment, and secondly just how little the IACV is actually needed anyway. I appreciate ambient temps are high at the moment but cold starts are truly excellent, the best they've ever been in fact. The engine does demand I hold the throttle open by just 3% for the first few seconds, but of late, and probably because I'm using the car every day, it doesn't even need that.
I run LPG 100% of the time and that includes cold starts, unlike petrol LPG does not condense on the internal walls of a cold inlet manifold which is the main reason we need cold start enrichment in the first place. Being a gas LPG mixes far better with air which of course is just another gas, so contrary to popular folk law you can cold start on LPG... indeed the car will cold start better on it, all you need is a good vaporiser like my excellent new Magic 3 Power that warms up incredibly quickly.
People may be surprised to see my cold start enrichment table now adds absolutely no additional fuel at all from 20 degrees coolant temp and above, and even below this enrichment is extremely minimal.
Compare this with a typical Lloyds Canems warm up enrichment table for a Chimaera running on petrol and an idle air control valve....
Obviously there are a number of advantages to being able to cold start without needing to chuck huge amounts of additional fuel down the neck of the engine, firstly there's the big saving in fuel and secondly you're not washing the oil off the bores and polluting the oil in the sump with raw un-burnt fuel.
I want to be 100% clear here, the Canems Dual Fuel system works brilliantly, and as any Range Rover or Discovery owner will tell you the old Rover V8 engine loves to run on gas. My Chimaera is no different, the car idles way better, drives noticeably smoother and cold starts significantly better on LPG than it or any other Chimaera does on petrol, the 53mpg petrol cost equivalent fuel economy is just the very very nice cherry on the cake.
The way I see it the IACV and the looping priming pulse it promotes is a small issue, with it disconnected the problem is 100% solved, and the valve removed completely the car actually runs and drives better too. As we roll into the cooler months no doubt the need for extra air for the first 30 seconds of cold start will become more apparent, but it's hardly beyond the whit of man to devise a very simple solution to cover that one off.
One electrically operated fast idle system I've always liked was the solenoid system on my old Chevrolet Caprice that ran a Holley carb on top of it's small block V8, when you put the air conditioning on it also energised the fast idle solenoid which just nudged the throttle lever on the carb a fraction to save a stall. This super simple system worked an absolute treat with no nasty auxiliary air bleed (vacuum leak) device required, it just cracks the throttle butterfly open a fraction and only at idle.
All that's required to fit a fast idle solenoid is a +12v supply, an earth, and a driver operated switch I would only ever need to use for those first 30 seconds of cold start, after that it can be switched off to return to my sealed plenum setup with the idle speed set on the butterfly rest position just as it is now. As I've proved, the engine only ever needs that small fast idle increase for the first 30 seconds or less during a cold start.
The Holley 4150 fast idle solenoid is just the ticket, I'd need to fab up a bracket and it'll be wise to use a fused relay, but there's a lot to be said for a super simple fast idle system like this which will completely remove the need for any air bleed type setup.
Obviously the throw of the fast idle solenoid is fixed, but you simply adjust how much the plunger nudges the throttle lever by winding the plunger in and out on its brass end nut, it's super simple, super adjustable.... and ultimately super effective
So today I removed my manual extra air valve I've been running for a few months now, I found it to be excellent and its taught me a huge amount about what the engine genuinely wants and needs in the way of extra air during warm up.
But my manual extra air valve was just a stop gap while I chased down and eliminated the earth loop that was causing my ECU to continually cycle the priming pulse feature, which was both frustrating and dangerous in equal measure.
The problematic no name pattern part idle valve that came with my Canems installation is shown on the left, it never worked properly so it just had to go.
I replaced it with another Bosch copy but a proper one this time made in Germany by Lowe who are a well respected ISO9001 certified manufacturer of idle valves and engine sensors.
As you can see I switched from the right angle to a parallel hose fitting type which allows for a far neater installation in the existing breather hose that originally fed the stepper motor.
This parallel type Bosch PWM idle valve was used on various Porsche models during the 1990s and is a direct replacement for the akward right angle type you get with a Canems installation. Placing it in the stepper motor feed hose means its only pulling clean filtered air, fitted like this and unlike the standard Canems idle valve setup no little add on after market filter is required.
Having corrected my earth loop I felt confident I could return to a quality PWM idle valve solution without stimulating the dreaded and dangerous looping priming pulse issue.... and I was right
The system now works exactly as it should and delivers a fully autonomous idle speed taper following my warm up idle valve duty table, unlike the valve that came with my Canems installation the German made unit from Lowe is a quality item that works exactly as an original Bosch part does.
My new idle valve was £50 purchased direct from the factory in Berlin including delivery to me here in the UK, by contrast an original Bosch parallel hose connector type Porche idle valve is £130 minimum, and thats if you're lucky enough to find one as they're now a rather rare part.... so mostly they are sold for a lot more than £130
Another victory for taking ownership of issues the installers of the engine management system were seemingly incapable of fixing themselves, as with so many things in life sometimes you just have to roll your sleeves up and sort things out properly yourself
But my manual extra air valve was just a stop gap while I chased down and eliminated the earth loop that was causing my ECU to continually cycle the priming pulse feature, which was both frustrating and dangerous in equal measure.
The problematic no name pattern part idle valve that came with my Canems installation is shown on the left, it never worked properly so it just had to go.
I replaced it with another Bosch copy but a proper one this time made in Germany by Lowe who are a well respected ISO9001 certified manufacturer of idle valves and engine sensors.
As you can see I switched from the right angle to a parallel hose fitting type which allows for a far neater installation in the existing breather hose that originally fed the stepper motor.
This parallel type Bosch PWM idle valve was used on various Porsche models during the 1990s and is a direct replacement for the akward right angle type you get with a Canems installation. Placing it in the stepper motor feed hose means its only pulling clean filtered air, fitted like this and unlike the standard Canems idle valve setup no little add on after market filter is required.
Having corrected my earth loop I felt confident I could return to a quality PWM idle valve solution without stimulating the dreaded and dangerous looping priming pulse issue.... and I was right
The system now works exactly as it should and delivers a fully autonomous idle speed taper following my warm up idle valve duty table, unlike the valve that came with my Canems installation the German made unit from Lowe is a quality item that works exactly as an original Bosch part does.
My new idle valve was £50 purchased direct from the factory in Berlin including delivery to me here in the UK, by contrast an original Bosch parallel hose connector type Porche idle valve is £130 minimum, and thats if you're lucky enough to find one as they're now a rather rare part.... so mostly they are sold for a lot more than £130
Another victory for taking ownership of issues the installers of the engine management system were seemingly incapable of fixing themselves, as with so many things in life sometimes you just have to roll your sleeves up and sort things out properly yourself
Thanks Al,
On early Canems installations like mine the installers fitted the idle valve close to the throttle bracket and gave it a little engine breather type filter, there's no real issues with this other than the fact the cheap pattern part idle valves they were using were not reliable.
Later on and still using the poor quality valve they switched to this idea.
In this set up the engine is pulling dirty crankcase gasses directly from the offside rocker cover flame trap through the pattern part no name idle valve, this gives the very real likelihood of the idle valve becoming internally coated in oil mist residue from the dirty crankcase gasses.
Of course the other end of this hose they've T'd into also ends at the plenum so what they've created is a loop under permanent vacuum at idle but no vacuum at wide open throttle and varying levels of vacuum everywhere in between. Not only must the valve have to pass dirty oil laden blowby gasses but it also has to cope with varying pressures across its inlet & outlet ports.
For a number of reasons, and not just for neatness, I would argue my placement of the idle valve and plumbing arrangement is far superior.
But even more important than this is the use of a quality idle valve in the first place, I believe the installers now fit a genuine Bosch idle valve presumably because like me they had a lot of trouble with the cheap poor quality one they continued to fit for years?
On early Canems installations like mine the installers fitted the idle valve close to the throttle bracket and gave it a little engine breather type filter, there's no real issues with this other than the fact the cheap pattern part idle valves they were using were not reliable.
Later on and still using the poor quality valve they switched to this idea.
In this set up the engine is pulling dirty crankcase gasses directly from the offside rocker cover flame trap through the pattern part no name idle valve, this gives the very real likelihood of the idle valve becoming internally coated in oil mist residue from the dirty crankcase gasses.
Of course the other end of this hose they've T'd into also ends at the plenum so what they've created is a loop under permanent vacuum at idle but no vacuum at wide open throttle and varying levels of vacuum everywhere in between. Not only must the valve have to pass dirty oil laden blowby gasses but it also has to cope with varying pressures across its inlet & outlet ports.
For a number of reasons, and not just for neatness, I would argue my placement of the idle valve and plumbing arrangement is far superior.
But even more important than this is the use of a quality idle valve in the first place, I believe the installers now fit a genuine Bosch idle valve presumably because like me they had a lot of trouble with the cheap poor quality one they continued to fit for years?
Sardonicus said:
So you now agree a Metered air leak is fine then Dave? proper job nice install
Thanks Simon. proper job nice install To be clear, and in my opinion, a small well controlled metered air bleed during warm up only is a necessary evil and even then only if the valve is of good quality..... and mistakes haven't been made elsewhere with the car's wiring that generate earth loops
A poor quality idle valve that delivers erratic and unpredictable behaviour is definitely far worse than no idle valve at all, just as it's impossible to tune a carburettor where a vacuum leak is present nothing makes tuning a EFI system more frustrating and ultimately impossible than an idle valve that's behaving erratically!
However, every cloud has a silver lining as my frustrating experience actually came with some real positives, for example my simple but highly effective manual extra air valve proved itself to be a fantastic way to learn precisely what the engine wants and indeed needs in the way of extra air during warm up. It also forced me to deep dive spark scatter closed loop idle control and develop strategies using this feature which when configured correctly very nearly completely eliminated the need for an idle valve of any type.
Keeping these spark scatter settings and combining them with a quality idle valve that works correctly and tuned to what I now know the engine wants in the way of extra air during warm up has allowed me to minimise its involvement, I remain a firm believer that when it comes to any sort of air bleed system the guiding principle is always 'Less is More'!
A sophisticated OEM ECU may well be able to offer effective closed loop idle management using an idle valve but in the case our comparatively simple engine management systems, and I include all the usual suspect RV8 TVR ECUs, you are way better off exclusively using the idle valve for adding extra air during warm up. After this if you want closed loop idle you're better off with spark scatter, and even during warm up if spark scatter is used correctly it is an excellent way to limit the amount of air bleed required from the idle valve which believe me is definitely the way to go.
For example by setting my base idle naturally high I can then use spark scatter to pull timing to bring the idle speed down to the target, but because spark scatter is not permitted to become active until 66c, during warm up and before 66c the naturally high idle base idle setting works to provide 90% of the addition engine speed required thus dramatically and almost completely removing the need for an idle valve. When I ran the car with no idle valve I proved by deploying the above strategy the amount of additional air required from my manual extra air valve was very small indeed, keeping this spark scatter strategy when I returned to quality made idle valve set up meant I could continue to benefit from less air bleed from the PWM valve during warm up.
Powers Performance do dot give you an idle valve with their MBE installation and I can see why, but there's no question without one there remains a small requirement for extra air during warm no matter what you do with spark scatter. Jules of Kits & Classics uses a Magneti Marelli stepper motor on his Emerald installations for warm up only, which knowing what I know now I would say is the ultimate solution. A series of steps is all you need, so keeping things simple by using a stepper motor is a good idea, saying that my PWM valve works just as well with a smooth controlled taper but I really don't think there's any significant advantage in using a rotary valve PWM IACV over a simple stepper motor system.
With idle valves the less you have to rely on them the better, they are necessary for a perfect OEM stable idle during warm up but with spark scatter they are not 100% essential, and if you do choose to use one for heavens sake make sure it's not one of the dreadful quality Chinese PWM idle valves that came with my Canems installation!
So far this German made one from Lowe seems to work perfectly .....
And selecting the Porsche parallel hose fitting valve rather than the more common right angle type permits a far neater installation.
The solution in my case was simply to remove the poor quality Chinese no name idle air control valve as supplied with my Canems installation and replace it with something better.
I didn't buy a Bosch original, I went with a German made copy from Lowe, I purchased it for £50 direct from the factory in Berlin including delivery to me here in the UK, and it works perfectly. I only use it for cold start, closed loop idle managed when the engine is warmed is handled by scatter spark, the two systems work together to deliver truly OEM idle management.
Original new old stock Lucas stepper motors are no longer available and the quality of the copies are a bit hit and miss from what I hear, so I would definitely consider replacing your old Lucas stepper motor with the Bosch rotary type idle air control valve from Lowe, for just £50 you get a brand new quality made infinitely variable valve your MegaSquirt system can control perfectly.
In my opinion its definitely worth investing £50 for a guaranteed solution
I didn't buy a Bosch original, I went with a German made copy from Lowe, I purchased it for £50 direct from the factory in Berlin including delivery to me here in the UK, and it works perfectly. I only use it for cold start, closed loop idle managed when the engine is warmed is handled by scatter spark, the two systems work together to deliver truly OEM idle management.
Original new old stock Lucas stepper motors are no longer available and the quality of the copies are a bit hit and miss from what I hear, so I would definitely consider replacing your old Lucas stepper motor with the Bosch rotary type idle air control valve from Lowe, for just £50 you get a brand new quality made infinitely variable valve your MegaSquirt system can control perfectly.
In my opinion its definitely worth investing £50 for a guaranteed solution
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