Idle Air Control Valves - Why I'm Not a Fan!
Discussion
I just wanted to interject at this point. May I start by saying this is in no way intended as a negative post and I hope it is taken in the spirit in which it is intended.
I don't think anyone would argue with the fact that some air leaks are undesirable, however there is a body of people (major manufacturers included before the widespread use of drive by wire) who seems to believe that having an idle valve is a good idea, and I am firmly in that camp.
We all now know Dave that you are , as of posting this thread, firmly in the opposite camp but constantly and sometimes quite vociferously putting forward one point of view isn't getting anyone anywhere. We are just all going to have to agree to disagree. Putting things in bold type just comes across as condescending. You're probably a lovely person in real life but the keyboard persona is at odds with this, again it's not a criticism it's just the way I read your posts, and by the look of some replies on the forums this view is held by others.
Another point I'd like to make is that some people (me included) may be having trouble with your timeline of events.
To me it seems to read:
1) My ecu install has given me a super smooth driving car, the combination of wideband fuelling, scatter spark ignition and idle control valve means that my idle is rock steady under all conditions even when the fans come on with their high power demands.
2) My car has developed an issue whereby the pre-start priming pulse energises every 2 seconds and the collective knowledge of myself and others involved has so far not deduced the underlying issue.
3) I have fixed the pre-start prime issue by disconnecting the idle valve (not actually fixed the fault, but it's had the desired effect on the multiple pre-start priming)
4) although previously I have said that the idle valve has been an important element in the previously described rock steady idle, I've now decided that I'm going to say I don't like idle valves and I'm going to post that it's an air leak and must be eliminated at all cost.
Now I will once again caveat this by saying this is NOT a dig and is NOT a negative post at anyone or anything, but anyone who follows your posts closely (which many do) will also possibly have noticed the same thing.
I myself have been guilty of putting forward points ad infinitum so I hope you take this in the spirit in which it is intended and maybe just accept that some very clever people with decades of experience on forums might just have a different point of view.
Getting the right tone in a forum post is often difficult so I very very much hope no-one is offended in any way by what I've written, if so I apologise now because my aim is harmony not conflict. I am going to make an effort to make sure any future posts I make will be in the spirit of co-operation.
I don't think anyone would argue with the fact that some air leaks are undesirable, however there is a body of people (major manufacturers included before the widespread use of drive by wire) who seems to believe that having an idle valve is a good idea, and I am firmly in that camp.
We all now know Dave that you are , as of posting this thread, firmly in the opposite camp but constantly and sometimes quite vociferously putting forward one point of view isn't getting anyone anywhere. We are just all going to have to agree to disagree. Putting things in bold type just comes across as condescending. You're probably a lovely person in real life but the keyboard persona is at odds with this, again it's not a criticism it's just the way I read your posts, and by the look of some replies on the forums this view is held by others.
Another point I'd like to make is that some people (me included) may be having trouble with your timeline of events.
To me it seems to read:
1) My ecu install has given me a super smooth driving car, the combination of wideband fuelling, scatter spark ignition and idle control valve means that my idle is rock steady under all conditions even when the fans come on with their high power demands.
2) My car has developed an issue whereby the pre-start priming pulse energises every 2 seconds and the collective knowledge of myself and others involved has so far not deduced the underlying issue.
3) I have fixed the pre-start prime issue by disconnecting the idle valve (not actually fixed the fault, but it's had the desired effect on the multiple pre-start priming)
4) although previously I have said that the idle valve has been an important element in the previously described rock steady idle, I've now decided that I'm going to say I don't like idle valves and I'm going to post that it's an air leak and must be eliminated at all cost.
Now I will once again caveat this by saying this is NOT a dig and is NOT a negative post at anyone or anything, but anyone who follows your posts closely (which many do) will also possibly have noticed the same thing.
I myself have been guilty of putting forward points ad infinitum so I hope you take this in the spirit in which it is intended and maybe just accept that some very clever people with decades of experience on forums might just have a different point of view.
Getting the right tone in a forum post is often difficult so I very very much hope no-one is offended in any way by what I've written, if so I apologise now because my aim is harmony not conflict. I am going to make an effort to make sure any future posts I make will be in the spirit of co-operation.
Edited by spitfire4v8 on Monday 23 July 10:38
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
There's a few things I dont understand in the post, but when you say your iacv is sat at 40percent duty that's not actually relating to airflow as such because of the way the valve works.
Bosch in their germanic wisdom have made the valves fail safe, such that if the valve has a power loss, or low signal, it flows a lot of air to force a fast idle / non-stalling scenario, certainly of the valves I have seen anyway.
The valve flows lots of air with no feed.
As you add signal the valve rotates, but the first part of the rotation closes the valve down from its fail safe position of high airflow to a point (somewhere around say 30 percent duty) where the valve is flowing at its lowest .. it's still not fully shut as there is always a tiny amount of bleed past on these valves, but pretty much shut to all intents and purposes.
Adding more signal from that point onwards progressively opens the valve again. So, the normal operating range for the valve would be from say 30% as a closed valve to say 80%plus as fully open (in airflow terms).
Your 40% duty cycle might only mean the valve is flowing 5% of it's capability, or less, it depends exactly how it reacts to the ecu's 80hz pwm signal which I think yours has, but moreover you should be able to target a duty cycle which has the valve pretty much flowing no air at all except for the tiny amount bleeding past the valve (tolerances to prevent is sticking presumably, but small tolerances so a small air bleed only).
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.
It seems a shame to do without the valve on your car as I firmly believe they have great benefits especially in winter, and had your priming pulse not been an issue then I would have suggested plumbing your valve into the area just after the throttle butterfly, that way when you were introducing air it would be in the same flow direction and position as the air from the throttle plate, so mimicking as closely as possible in terms of plenum airflow the effect of adding such airflow from actual butterfly opening.
I don't know how hard it would be but maybe David at Canems could alter your ecu to run a stepper motor so you could see if that brings you the best of both worlds, a fast idle for winter starts where you'll be running slightly richer anyway through warmup so if you're worried about introducing shunting issues this should mask it, then fully shut off at high temps so you can run your car exactly as it is now in its warmed up state?
Or of course you could upgrade to drive by wire .. I've done this before by keeping the original pedal and cable to the throttle but chop it in the engine bay, the pedal cable now controls a pedal position sensor ( a honda item was used as this is how they used to do it, and if it's good enough for honda!) , and an actuator pulls on the cable to the butterfly .. you get all the benefits of drive by wire, but you get to keep your existing pedal box and plenum actuation so keeping costs to a minimum.
Bosch in their germanic wisdom have made the valves fail safe, such that if the valve has a power loss, or low signal, it flows a lot of air to force a fast idle / non-stalling scenario, certainly of the valves I have seen anyway.
The valve flows lots of air with no feed.
As you add signal the valve rotates, but the first part of the rotation closes the valve down from its fail safe position of high airflow to a point (somewhere around say 30 percent duty) where the valve is flowing at its lowest .. it's still not fully shut as there is always a tiny amount of bleed past on these valves, but pretty much shut to all intents and purposes.
Adding more signal from that point onwards progressively opens the valve again. So, the normal operating range for the valve would be from say 30% as a closed valve to say 80%plus as fully open (in airflow terms).
Your 40% duty cycle might only mean the valve is flowing 5% of it's capability, or less, it depends exactly how it reacts to the ecu's 80hz pwm signal which I think yours has, but moreover you should be able to target a duty cycle which has the valve pretty much flowing no air at all except for the tiny amount bleeding past the valve (tolerances to prevent is sticking presumably, but small tolerances so a small air bleed only).
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.
It seems a shame to do without the valve on your car as I firmly believe they have great benefits especially in winter, and had your priming pulse not been an issue then I would have suggested plumbing your valve into the area just after the throttle butterfly, that way when you were introducing air it would be in the same flow direction and position as the air from the throttle plate, so mimicking as closely as possible in terms of plenum airflow the effect of adding such airflow from actual butterfly opening.
I don't know how hard it would be but maybe David at Canems could alter your ecu to run a stepper motor so you could see if that brings you the best of both worlds, a fast idle for winter starts where you'll be running slightly richer anyway through warmup so if you're worried about introducing shunting issues this should mask it, then fully shut off at high temps so you can run your car exactly as it is now in its warmed up state?
Or of course you could upgrade to drive by wire .. I've done this before by keeping the original pedal and cable to the throttle but chop it in the engine bay, the pedal cable now controls a pedal position sensor ( a honda item was used as this is how they used to do it, and if it's good enough for honda!) , and an actuator pulls on the cable to the butterfly .. you get all the benefits of drive by wire, but you get to keep your existing pedal box and plenum actuation so keeping costs to a minimum.
ChimpOnGas said:
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.
And the IACV is a "vacuum leak" used to control engine speed at idle, when the main "vacuum leak" is closed.ChimpOnGas said:
An internal combustion engine is just a big vacuum pump,
100% incorrect. An ICE is a prime mover; a source of mechanical energy. Creating a vacuum is not the purpose of an ICE, it is simply a side effect of the simplest and most common method of controlling power output (throttling). Additionaly no vacuum will be created in a throttled engine when run at WOT, and a diesel engine doesn't create a manifold vacuum at all.ChimpOnGas said:
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
No, there is metered air and unmetered air. Unmetered is always uncontrolled, metered air could be uncontrolled (in the case of a speed density system). The air passed by the IACV is controlled (by the ECU) and metered.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
ChimpOnGas said:
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.
The carbon canister purge valve is not uncontrolled, the ECU controls it. Both this and the crankcase ventilation system are irrelevant, the gasses from both are metered.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.
ChimpOnGas said:
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!
100% incorrect, this goes right to the core of your misunderstanding. The amount of air required for an engine to idle correctly over the entire expected coolant temperature range, and with the varying loads applied by alternator and aircon etc. varies significantly. A fixed throttle opening (sorry, "vacuum leak") can not hope to control idle correctly in all these conditions, which is why a secondary throttle is fitted; the IACV. Variable ignition timing can be used to control idle to some extent in the absence of an IACV, but control range is limited, and also results in undesirable side effects such as overheating at idle with a hot engine (retarded ignition) and higher emissions with a loaded engine.ChimpOnGas said:
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 
No, this is yet another misconception. Air is air, irrespective of whether it comes through the main throttle or the IAVC; the total amount of air is metered and fuel added accordingly. The presence of an IACV will not spoil your throttle response, unless the ECU has been programmed to do this.ChimpOnGas said:
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.
More misconceptions; I think you are confusing yourself. If the air is metered then it makes no difference. Many millions of production cars with perfectly functional idle control systems prove you wrong.ChimpOnGas said:
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?
This goes back to the original source of your confusion; you keep calling the air that passes the IACV as uncontrolled, when this is clearly not the case, it is controlled by the ECU. Genuine vacuum leaks (i.e. not through control elements such as the throttle or IACV) are uncontrolled.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?
ChimpOnGas said:
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.
You are taught to fix vacuum leaks because they are uncontrolled, and may also be permitting unmetered air into the engine. This is quite obviously not the same as an IACV which is both controlled and passes metered air.ChimpOnGas said:
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!
As I may have mentioned, you have a fundamental misunderstanding of the purpose and operation of the idle control system in a fuel injected engine. If you can get past the idea that it is an uncontrolled vacuum leak things should click into place.
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
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
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
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
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
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
Why on a performance car would anyone be bothered about raised idle!
I thought that was for daily drivers!
Maybe thicker oils make these first few seconds more of a challenge but this is my point, it’s a car with a big cam anyway, my biggest issue has always been rattle on start up from cam train, with my car not using an idle control valve I now have control of those first few critical seconds when the engine first fires up.
Almost exactly as Dave describes 3/5% throttle is more than enough to raise idle, I’m able to progressively bring it up from 800-1200 revs which avoids clattering cam from revs being to high for the first say 10 seconds,,,, I love this fact.
Also I’ve driven a few Tvr with idle valves such as the Bosch and it’s like the throttles still open even when it’s shut, bloody auto feel to it.
Ok it smoothes out poor driver input but if you like to have instant on/ off throttle like a true thouroughbred imo you don’t want idle valves getting in the way.
I’ve driven on the worst winter morning with cold wet -7/10d and within 2 minutes of driving the engine holds an idle of about 800 so if the cold start map has decent mapping enrichment it seems to make zero difference without the valve on my car.
The fact it uses about half a gallon less every start up is as Dave mentions another big bonus, all that fuel sloshing about thinning your oil can’t be good.
I slowly lose the need to defend my car or it’s ( options) and just thank f
k I did something right with it.
I’m not much of a mechanic but all along something told name getting rid of the stepper was a wise move because reading up on how it’s operated on the CUX is complicated enough and my thoughts were after market Ecu probably have less data to go on so infact its use might be a bit more clumsy.
It’s obvious they work well but it’s a lot of extra complication on a very basic engine and if like me you want Performance over smoothed out throttle action that I’m not actively controlling then you,don’t need it at all.
The final reason why I think we Performance car owners should not have one is because it feels sooo much better. More organic and natural.
I might add a choke cable for fun, so the next owner can have this so important raised bloody idle
see I like a manual choke,,,,
That’s it, when I was a lad an old boy said get the choke off ASAP and your engine will last longer and need less choke throughout its life, so I became that way, soon as the buggers were fired up I’d be trying to run it with a light throttle idle and remove choke to the point it wants to stall then just enrichen it a tad... which is sort of how I see my Mbe car behaving, there’s more than enough enrichment on cold days in the mapping.
My engine note changes when slowing down using a prolonged off throttle pedal which suggests it’s adding and taking fuel out there too. Clever stuff.
It’s the closest thing to a motorbike throttle I could get and that brings many joys in itself.
It’s the only reason I hesitate to let the car be sold, I know it will last decades in this guise. .
I thought that was for daily drivers!
Maybe thicker oils make these first few seconds more of a challenge but this is my point, it’s a car with a big cam anyway, my biggest issue has always been rattle on start up from cam train, with my car not using an idle control valve I now have control of those first few critical seconds when the engine first fires up.
Almost exactly as Dave describes 3/5% throttle is more than enough to raise idle, I’m able to progressively bring it up from 800-1200 revs which avoids clattering cam from revs being to high for the first say 10 seconds,,,, I love this fact.
Also I’ve driven a few Tvr with idle valves such as the Bosch and it’s like the throttles still open even when it’s shut, bloody auto feel to it.
Ok it smoothes out poor driver input but if you like to have instant on/ off throttle like a true thouroughbred imo you don’t want idle valves getting in the way.
I’ve driven on the worst winter morning with cold wet -7/10d and within 2 minutes of driving the engine holds an idle of about 800 so if the cold start map has decent mapping enrichment it seems to make zero difference without the valve on my car.
The fact it uses about half a gallon less every start up
is as Dave mentions another big bonus, all that fuel sloshing about thinning your oil can’t be good. I slowly lose the need to defend my car or it’s ( options) and just thank f
k I did something right with it. I’m not much of a mechanic but all along something told name getting rid of the stepper was a wise move because reading up on how it’s operated on the CUX is complicated enough and my thoughts were after market Ecu probably have less data to go on so infact its use might be a bit more clumsy.
It’s obvious they work well but it’s a lot of extra complication on a very basic engine and if like me you want Performance over smoothed out throttle action that I’m not actively controlling then you,don’t need it at all.
The final reason why I think we Performance car owners should not have one is because it feels sooo much better. More organic and natural.
I might add a choke cable for fun, so the next owner can have this so important raised bloody idle
see I like a manual choke,,,, That’s it, when I was a lad an old boy said get the choke off ASAP and your engine will last longer and need less choke throughout its life, so I became that way, soon as the buggers were fired up I’d be trying to run it with a light throttle idle and remove choke to the point it wants to stall then just enrichen it a tad... which is sort of how I see my Mbe car behaving, there’s more than enough enrichment on cold days in the mapping.
My engine note changes when slowing down using a prolonged off throttle pedal which suggests it’s adding and taking fuel out there too. Clever stuff.
It’s the closest thing to a motorbike throttle I could get and that brings many joys in itself.
It’s the only reason I hesitate to let the car be sold, I know it will last decades in this guise. .
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
I agree with Simon on this one. Kudos to you for working through the issues and finding a work around but I would have expected more from the supplier and manufacutruer in this instance. I do not fully understand the technicalities of IACV or stepper motors but it does sound like you have put in place a work around when there is still a root cause? The 28 year old 14CUX runs a stepper motor fine and so sure Canems should have no issues being a modern ECU. 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 I would be tempted to chuck this back at either Lloyds or Canems to resolve, sounds like something is not right.
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.
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