Cold engine = Problems

[X2Xtreme360]

When the engine is started cold (it's worse when the outside temperature is colder) the engine will stall once in a while. Not all the time, but in particular, going in 1st from 2500-3000rpm then clutch to shift. The RPM's will drop pretty quickly when the clutch pedal is depressed, and sometimes (only on a cold engine) the engine will shut off. I'm guess I should clean the IAT sensor, but what else could it be if that's not the problem?

[elon3kgtslowner]

yeah that sounds almost exactly like the problem i had with my car. it stalled when i clutched in one day rolling to a stop sign and it sent me into a curb and i bent a rim. i've been trying to get to the bottom of it since. i upped my idle in the mean time so now it just kinda drops rpms suddenly but the idle is fast enough that it wont stall anymore. i'll be keeping an eye on this thread now and hopefully someone has some ideas. btw, mine does this warm too sometimes so i didn't consider IAT sensor. do u know how to clean it?

[Igovert500]

What model car do you have? What is your warm idle, what is your cold idle? I'd guess you have problems with the Fast Air Idle Valve. Do a search, I've posted on it before.

[X2Xtreme360]

I have a 94 DOHC N/A. The idle is fairly consistant. At cold it usually sits a little lower I'll say around 7-800. When warm it's at 1000 and once in a while a little high at 1200. I had a check engine light on, come to find out it had to do with the EGR system, which if the valve is stuck open that can cause a rough idle on a cold engine. They reset the light and it hasn't come on in a few days. Other than that all I have seen so far is a crack in the PCV breather, but I don't think that plays a role in a rough idle. I was planning on an engine dress up kit, so then I could replace all hoses, and also probably replace all gaskets and O rings around the injectors.

[Linebckr49]

might as well get rid of the EGR system while your under the hood. check the FAQ thread, it has info how to do it properly so you don't get a check engine light.

[thunderchicken2]

I have somewhat of the same problem with my 91. At any temperature it will idle really high warm at around 2000 and cold sometimes 3, and will eventually come back down. If i try to take off without it warming up, it will stall out around 2500 rpm but has never shut off..

[Igovert500]

Ok, this is why I dislike 3 people asking questions in the same thread, it's harder to address different problems. So everybody clean your IAC, after that if the problem isn't fixed, start your own thread. Idling problems can be caused by dozens of diffferent things, and it's just easier to diagnose if we aren't constantly mixing your cars up.

Cleaning IAC
You can also do a search for 'IAC' as this topic comes up every 3 days.

Back to the original poster:

Originally Posted by X2Xtreme360

I At cold it usually sits a little lower I'll say around 7-800. When warm it's at 1000 and once in a while a little high at 1200.

That's odd, it should idle higher when cold. The Fast Idle Air Valve is the part of your throttle body with coolant lines running through it. The fast idle air valve is open when the throttle body is cold and bypasses enough air around the butterfly to increase the idle speed to 1500-2000 rpm. With the coolant lines connected and flowing properly, the valve warms up pretty quickly and closes, and the idle speed drops to normal ~700rpms. If the FIAV isn't seeing the coolant temp increase it could be staying open the entire time.

Run the car, is the lower part of the throttle body cool or hot to the touch? If cool it suggests the valve is staying open. Check your coolant. Make sure a) it is at the right level, b) it isn't mixed with oil (oil would be milky and have bubbles) c) make sure the flow of coolant isn't blocked. d) make sure the coolant lines running to the TB aren't broken.

Also, check for plenum and vacuum leaks. I'd replace that breather hose as well. The stalling suggests a large leak or the MAS isn't plugged in. So eliminate all obvious leaks/cracks, etc. first and foremost.