Very low idle and stumble when start the engine. Please help.

[areznik]

Hey Guys, I need your help!

I have Q45 '94 with new MAF, BG44K every two months, 2 year old fuel pump, new KS, clean TB (did under plenum job last April), clean IAC, 4 months old NGK OEM plugs, 3 year old injectors (all 8).

I have read through numerous posts but still don't know what to do. Here is the situation:

In a cold start everything is fine, it idles around 1200 rpms but once it gets worm the idle in park drops to 450!! If I put in drive it drops to 400!! If I attempt to start the engine when its hot then it will die in a second or two. Sometimes it struggles not to die and eventually the rpms move to 450 but more often than not it will die if I don't help it with a gas pedal. When I help it with the pedal it will eventually remain steady at 450. The car drives fine, and even in idle it is very smooth at 450 rpms. Never had this problem before and it appear actually about two weeks ago.

My thought intially was an air leak as I hear a hissing sound from the engine, but then why the problem occurs only when the engine is hot? It seems more like an electrical problem unless I am wrong and I need your wisdom here.

This coming month I am very dependent on my baby Q as I have to drive everyday to work and cannot afford it to misbehave at me during this time.

Your suggestions would be greatly appreciated,Andre.

[elwesso]

Hey Andre, did you end up going to the F1 race??

Anyway, about your problem.... When you adjusted the IAC, did you unscrew the little thing 2 turns out from all the way in?

I think you probably have an air leak as well... in my experience on the Q, air leaks past the MAF cause the idle to be lower, not higher.....

My old Q had this same problem sans the low idle.. At hot startup it would sometimes die, but then it would start right back up.... Unfortunately it died forever beforeI could find the culprit...

Someone had mentioned to me things like the coolant sensor (is yours a federal or california model?)

The reason it doesnt happen when its cold is because everythign is preset on a cold startup... The fuel, timing, and so on... until the coolant reaches 176 or so, the computer adjusts everything by a baseline.. If I understand correctly (take with appropriate grain of salt), once the engine reaches operating temperature, the computer tries to maintain a steady idle, and it assumes you have the baseline IAC set correctly.... Meaning that when you unplug the IAC, RPM should drop 50-100 RPM... Basically, the engine is supposed to idle pretty much perfect and then the IAC is used to make it even more perfect and smooth, and to make it unnoticeable when you turn on the AC and things of that nature...

I would try bumping the IAC up a little bit and see what that does.... Does it do it every time?

[areznik]

Hey Wes! I did not go to the Race eventually, too busy with my internship. Maybe next summer ... . I will let you know for sure.

About my problem, I did play with the IAC screw and it always used to be 2.5 turns out. Also, it is very interesting that unscreweing that screw alsmost does not have any effect on rpms.

Also, I think my Q runs rich because yesterday it was hot and I could see the white smoke from the pipe. It probably points to an air leak where computer thinks that it gets more air than it really gets ... and therefore runs rich. What is the best way to find an air leak?

[elwesso]

If its that big, what I would do is start calling around to local mechanics and see if they have a smoke machine.... What it does is inject this smoke stuff (similar to party smoke) and you just watch where it comes out..... I think this method owrks better than finding it with brake parts cleaner or any of that other junk, this locates it on the spot.....

[DAEDALUS]

Usually ECU-controlled richness is indicated by a lot of black soot coming from the pipe. White smoke is reserved for large injector seal leaks and pooling gasoline. Unless it happens for a bit at startup only--then it could be a slow leak that pools after the last shutdown.Air leaks always leak into the intake, not out, unless forced induction is present. All gasses will move from high pressure to low pressure.

[MattB]

Sometimes just cleaning the IAC doesn't do the job-my G20 had a similar problem which was fixed by replacing the IAC valve altogether.

[areznik]

Wouldn't computer throw a code if there was such a bad injector leak?

[DAEDALUS]

There is a code assigned to injector leaks. A slow leak that smokes only at startup probably wouldn't last long enough to throw a code. I wasn't suggesting it was an injector leak, just that the logic of an air leak causing richness is flawed, unless the ECU goes into a failsafe mode, ignoring MAF. That would throw a code as well. But not many things cause white exhaust. Either steam (water or coolant) or gasoline. You said you cleaned the IAC--that was after this problem showed up? A Consult at the dealer can manually operate the IAC to help troubleshoot.