Idle Air Control Valves - Why I'm Not a Fan!

Idle Air Control Valves - Why I'm Not a Fan!

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ChimpOnGas

Original Poster:

9,637 posts

178 months

Thursday 19th July 2018
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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 yes

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 scratchchin

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.. wink




Edited by ChimpOnGas on Thursday 19th July 14:30

carsy

3,018 posts

164 months

Thursday 19th July 2018
quotequote all
I take it youve had to set the throttle a bit more open to help it run when cold as well as the ecu ramping the timing up to its max.

Because of this i suspect the ecu will pull the timing when warm to keep your tick over at the correct rpm. So what timing are you now running when warm. Im guessing a lot less than your original 18 -20 degrees.

ChimpOnGas

Original Poster:

9,637 posts

178 months

Thursday 19th July 2018
quotequote all
You're not just a pretty face Ian wink

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!


Classic Chim

12,424 posts

148 months

Thursday 19th July 2018
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Your not helping,,,,
I’m trying very hard to sell my MBE equipped car, Well I would be if I advertised it biggrin
I’ve even tried to ween myself off it, on axle stands and engine switched off for over a month now, feels like a year and as I know how well they drive without idle valves I decided to try it today after reading this.
Assumed battery would be flat and pump priming sounded sluggish but immediately she fired into life and after less than 20 seconds later after clearing her throat, 800 rock steady idle.
Fell in love again, fk st crap.

I can only agree with everything said here, my RV8 is so much happier without idle or stepper motor interference. Of all the mods or things I’ve replaced for new
This is the one I’ll miss or more the point makes it so hard to sell because it is so exciting when they run so sweet.
3 years this month coming since MBE installed. Faultless and seems to get better if anything.
Between Mbe and Powers they’ve got it worked out on this one.
One of my better decisions in life,,,, as long as I keep it scratchchin



carsy

3,018 posts

164 months

Thursday 19th July 2018
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You seriously getting rid Alun.

What about your head porting project , you need the car for those surely.

Classic Chim

12,424 posts

148 months

Friday 20th July 2018
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Hi Ian, I’ve rough ported one head on the inlet side but a combination of back problems and not enough income coming in has stopped me in my tracks basically.
My prospects are not looking great so Tvr stuff for the first time has to take a back seat and when that happens I start to see it as a weight rather than a pleasure.
Needs outriggers to be a good car for years to come but even 2k is more then I can spend which starts me thinking it’s time for someone else to own it or just do like others have done, moth ball it until I’m better off.

I’ve had a mate suggest he can do the welding but then blew cold, I think he’s going through problems himself and probably under estimated the work involved, he worked for a few Tvr men back in the day so find it a bit odd as I think riggers is more a pain in the arse than difficult!

Everyday is a new day so hope lives eternal. Going without a Tvr during this warm spell, just about as bad as it gets biggrin

spitfire4v8

3,990 posts

180 months

Friday 20th July 2018
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One of the reasons I've stuck with emerald for the last 15 years is that they just work. The magnetti marelli stepper style IACV works. The idle stabilisation off the timing works. The adaptive fuelling works. The triple independant maps work. The drive by wire throttle works. I've never had an ecu failure in those 15 years either (there's been other things, but not an ecu failure). The only think I don't know if works or not is the traction control because no-one's ever asked me to do it lol.

I always advise an IACV (though not everyone wants one, wrongly in my opinion) .

Whilst it's true that any air that's not accounted for is bad (and I've come up through the same older car route as you have Dave and come across the same wily old foxes that used to tune them) , I think it's important to not get too carried away with the difference between an unmetered air leak on an old carb'd engine v something like an IACV which can be correctly accounted for in the ecu setings. I just don't see the issues you've come up against Dave and my opinion is that if people start deciding they don't want an IACV based on this thread then they're going to be missing out on its valuable work during startup and warm up. It just needs setting up properly as long as the ecu allows it.

spitfire4v8

3,990 posts

180 months

Friday 20th July 2018
quotequote all
Alun, as a fellow bad back sufferer I quite literally feel your pain!
I've got two of my TVRs mothballed at the moment, one because I can't affrd the money or time to devote to it, the other because I've not got room for it at work. I don't intend to sell either of them though so think hard before deciding to sell .. it will always be harder to buy something of the same spec back in the future! Keep telling yourself they're an investment (though that was hard to tell myself when my cerb cost me 8k in the first year haha!) best wishes smile

ChimpOnGas

Original Poster:

9,637 posts

178 months

Friday 20th July 2018
quotequote all
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 smile 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 scratchchin not knocking the Canems they can all have their foibles but I think you have another issue your masking by disconnection frown fixing the symptom rather than the actual problem , Alun sorry to hear your news fella eek this forum would definitely suffer without your input and good humour frown
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.

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 scratchchin

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 rolleyes

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 yes

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 rolleyes. 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.



motul1974

721 posts

138 months

Friday 20th July 2018
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Sorry to it hijack the thread, BUT, Mark Adams contacted me today to ask if I was staying with the Lucas set up or switching to the ACT TPS for my new GEMS loom he's doing.....I hadn't really thought about it much.

Sounding like given my planned set up, an upgraded version may be the way to go??????

carsy

3,018 posts

164 months

Friday 20th July 2018
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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.

Maybe this is why the Emerald only uses the idle valve for cold starts. Once up to 70 degrees thats mine done and it just stays at that setting unless temps drop below 70 degrees. It does not come into play at all during idle mode.

Im just struggling to see how air entering the plenum from 2 different places, IF fueled correctly and like i say once warm my idle valve is a fixed setting, can cause running issues albeit small issues.

Not saying your wrong Dave as you have a clear improvement but maybe your valve and ecu werent playing together. Who knows.

Anyway glad youve sorted things i may give it a go at some point just to see.

jazzdude

900 posts

151 months

Saturday 21st July 2018
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Can the 14cux work without a stepper and some of that aftermarket ignition wizardry you describe Dave?

What about PAS at full lock and A/C compressor turning on / off ?

As far as I am aware, the stepper stops it stalling on mine, adjusting the drop in idle for both, even on a warm engine.

ChimpOnGas

Original Poster:

9,637 posts

178 months

Saturday 21st July 2018
quotequote all
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 nono

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

18,928 posts

220 months

Saturday 21st July 2018
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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 wink just a heads up wavey

ChimpOnGas

Original Poster:

9,637 posts

178 months

Saturday 21st July 2018
quotequote all
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 wink just a heads up wavey
Yes, of course Simon, it takes seconds with the Canems system, it's super easy.

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

20,143 posts

254 months

Saturday 21st July 2018
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ChimpOnGas said:
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 yes

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!
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.


stevesprint

1,114 posts

178 months

Saturday 21st July 2018
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Quote from https://www.pistonheads.com/gassing/topic.asp?h=0&...
carsy said:
Ive fitted a Bosch 2 wire idle valve. It fits in the original stepper feed pipe. I just cut a small section out of the stepper feed pipe and it fits in perfect as if it was designed for it. I'll try n find a picture.

Id say you only need an idle valve for cold starts. If your happy to hold the throttle open a touch for a minute or two from cold then you probably dont need one as long as your cold mapping is up to scratch. I ran without one for a while but its so much easier with one from cold.

I have an Emerald and it doesnt have closed loop idle control. You can only map the idle valve against temperature. So when your up to normal temp thats it the idle valve has no further use. Having said that with the spark scatter feature enabled my idle is rock solid, doesnt dip with fans coming on or power steeting etc. Infact if your spark timing is bob on at idle, and either side of idle you dont really need spark scatter.

Id personally say One lambda sensor is enough in the Y piece.

Sounds like your talking yourself into it. !!!
Sounds like Carsy's Emerald has the best of both worlds, “So when your up to normal temp thats it the idle valve has no further use.”

Carsy, do you know if your idle valve closes completely when up to temperature?

ChimpOnGas

Original Poster:

9,637 posts

178 months

Sunday 22nd July 2018
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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

20,143 posts

254 months

Sunday 22nd July 2018
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ChimpOnGas said:
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.
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.

ChimpOnGas

Original Poster:

9,637 posts

178 months

Monday 23rd July 2018
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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.


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 rolleyes.

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? rolleyes

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 yes

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!