Idle Air Control Valve explanation needed?

[Meestahbig]

Hi,

I'm still chasing my very intermittent stall. It only happens when braking and transitioning from open throttle to idle. I only recently noticed RPM bouncing a bit when it drops below 1000 RPM on slowing down. I have no codes and no engine lights. I cleaned the IACV and reinstalled but the problem came back relatively soon.

I saw one article on here about a teardown of the unit, but I can't seem to find it again. I searched for the past 30 minutes.

So my question is does anyone know what actually causes it to trigger an engine code or light? I highly doubt there is a "end of stroke" switch in either direction which tells the system it's actually open or closed. So if the unit is shorted or circuit is open, ok, I can see how it throws an error. If it's stuck one way or the other and the system recognizes car is running rich or lean, ok. But if the thing is just not swinging open 1/500 times when decelerating and causing a stall - it seems like this could elude the check engine light!

Anyone care to provide their 2 cents.

I'm going to swap the part with a URO aftermarket piece. Might not last 200k miles, but should be good enough to know - even if it lasts a year.

High speed, no issues. Only on off throttle, when decelerating. Never misfires at idle (once it's idling). I've swapped many sensors, and some of them more than once. Swapped fuel pump and MAF.

Thanks.

[80stech]

The idle control valve doesn't really affect mixture. The DME knows how fast the engine should be running according to other inputs such as the MAF and accelerator pedal so if that doesn't make sense it might set a code. Setting a code doesn't mean it lights the CEL. I wouldn't go with the URO IAC valve more because it might not work properly right off the bat and add to the confusion, not so much about how long it might last. We had someone here have trouble with exactly that a while back and I think we went through some of that in your other thread. What have you done since you left off from the other thread??

[Meestahbig]

Thanks. I put on a new OEM BMW crankshaft sensor, swapped fuel pump, swapped MAF. Camshaft sensors replaced by mechanic while I was having surgery.

I did clean the IACV but didnt relubricate it. I recently saw the bouncing idle when slowing to a stop. The stall only happens when slowing down to a near stop. Always in transition to idle and only very rarely. Like 100+ times it's fine, then it stalls with basically no warning.

Mechanic said nothing else we can do, so I've returned back to the IACV.

You know pelican parts sells the URO brand IACV, so I don't think it's total crap.

[Meestahbig]

I'm by no means an expert, but it just seems logical to me given the stuff I've already replaced and now seeing it stall a few times. I'm figuring if I had a vac leak somewhere it would cause issues while idling, but I have no issues when idling as long as the car gets to idle, it's when it's transitioning that it may or may not die bc the valve in my mind isn't always opening. The valve is moving around over and over and over. Hundreds of times I imagine in stop and go traffic. I also had mechanic do a smoke test and car didn't have an issue.

[X5chemist]

Check the DISA valve seal. What are your fuel trims? What are the O2 sensors reading? Readings there will tell you if unmetered air is getting into the combustion chamber.

[Meestahbig]

DISA valve seal is relatively new with OEM part. I never check the oxygen sensors and I only have an OBD2, so not sure I can check with this, but my gas mileage is bang on great. Smoke test, good gas mileage and no misfires, make it hard to think there is a air leak. Highway like 26mph, combined it's like 21 and I live in a high traffic state. I've reset the Cons 1 & 2 frequently since this all started bc I like to monitor this. My engine is great and strong, but sadly if new IACV doesn't resolve this, it's game over and I'll start working on my 2006, reluctantly. I really don't need both, but wanted to drive the 2003 until failure.

Merry Christmas all.

[Salty B.]

Originally Posted by X5chemist

Check the DISA valve seal. What are your fuel trims? What are the O2 sensors reading? Readings there will tell you if unmetered air is getting into the combustion chamber.

In my case, a sticky IAC valve was causing these O2 sensor errors and codes. I had no other symptoms; smooth idle, no hesistations.

Removed it and cleaned it with MAF cleaner, no more codes. But getting that thing back in... well at least all the cuts have healed now.

[Meestahbig]

New IACV is in. Will drive and see how the rpms go off throttle. Old IACV - I cleaned it not long ago, but now I realize it's shot. Dirty and still rattles but nothing like the new one. Old one is gitty inside and I can feel it hanging when I rattle it to swing the inside around. So - let's see. I'm hopeful as usual, but this makes sense. In the past when my cam sensors were going, the car stalled only on turning. This time was in straight line decelerating off throttle, and also sometimes going into parking space.

[80stech]

This is the one that you used the carb cleaner on right? That's what happens, the carb cleaner swells the seals and makes it sticky.

[Meestahbig]

Yes sir. I used carb cleaner. It must have been sticking before, but then I made it worse
Which actually helped me out anyway. One short trip so far and car was fine. I'll update here and close my other thread once I drive a 1000 miles. Thank you and all the other, I really appreciate the online comradery and help.