92 Supreme 3.1L stall at idle- HELP

Runs strong, no trbl codes, replaced IAC. The 3.1L still stalls at idle when warm. Actually, the tach shows idle at 800RPM, then starts to osscillate from 1K to 500 then stalls! Any ideas??

UT OH!!!

It runs ok until it warms up?

If the car is running fine in closed loop(running using pre determined information from the prom), and then starts stalling when it switches to open loop(running using information from the sensors) that usually indicates the ecm is having trouble deciphering the information from all of the sensors. It's not a cheap fix but it is my best guess from the way you describe the way the car runs.

Good luck and hope this helps.

Does it start ok? could be a bad EGR valve.

If the ECM is having trouble, you may try disconnecting the battery for 5 or 10 minutes. This will force the ECM to loose all of its learned information, reset the IAC, reset the fuel pulse width to default, etc. Although if the ECM isn't setting any codes, I doubt it is the root cause of the problem. They are usually pretty good about detecting errors that relate to idle problems (or any thing else that could impact emissions)

When ever you disconnect the battery or replace the IAC motor it needs to be reset! The reason the idle is surging is because the ECM does not know where to position the IAC pintle. There are 2 ways to learn the IAC setting one is using the GM scan tool to perform the function, the other is to let it idle for a couple of minutes in drive and then in park. Sometimes this works but it is easier to use the scanner. Call a dealer and ask how much they charge to relearn the IAC. In my shop we charge 30 minutes of labor for this.