this is what ive got.... when i first start the car, the idle jumps way up and slowly comes down, it also does this when i push in the clutch. it takes about 10 to 30 seconds to come down to normal idle speed. its worse when cold, but does it all the time. ive replaced the IAC valve and the MAT sensor. i checked all the vacuum lines, ok. i sprayed carb cleaner all over the entire intake and vacuum line system, nothing. im wondering if a bad MAF sensor could be the problem, although there is no code for it. if it could be, how do i test it to check? i did the "tap" test, it didnt make the idle change one bit. ive asked a few older GM techs i know and they are kinda stumped as well. anyone have any thoughts?

 

Still fighting that one, Doc? I wish I had some revelation, but nothing new has popped into my cranium.

I suppose the MAF could be errant, but the control of the engine is so dependent on the MAF input that the ECM watches it pretty closely. The ECM will only tolerate MAF errors for about 600mS before setting a code. That timer is in the programming.

I'd be more suspicious of a vacuum leak somewhere, like an EGR valve being ported open inadvertently, brake booster leak, or a binding throttle shaft/plates. I seem to recall that we've been all over the IAC system in the last episode.

If you haven't already done so, I'd suggest temporarily disabling the EGR by disconnecting (and plugging) the vacuum source line to the EGR solenoid.

You might also disconnect teh throttle cables and assist springs from the throttle body, and manually operate teh throttle through its range several trimes to check for binding. Try moving the shaft in different directions to see if you can induce some sticking or binding.

I hope someone else can offer better advice.