My 91 3.1 has an idle speed of about 1000 rpm. Its also kind of rough at idle and seems to lack power at low revs. I tried adjusting the idle as it describes in the manual- turning the minimum air screw with the IAC disconected. However with the IAC disconected the idle drops so low the motor won't run. I've heard the 3.1 needs a sensor conected in order to re-set the ECM for the correct idle. Is that correct? Also what else should I check.

Thanks

 

You should open up the idle screw until the engine DOES run normally with the IAC disconnected. Then, let the engine warm up, and adjust the screw until the tach reads around 800 RPM (due to the inaccuracy of it). Shut the engine off, and plug the IAC back in. The idle speed should jump a bit, then settle back down to just above or at where you set the screw. When cold, your IAC should be idling the engine around 1200-1300 RPM, to help it warm up faster.

 

The GM service manual for our cars says you need the Tech 1 "scan tool" for setting the IAC position for minimum idle speed. I thought there was no way around this. Glad I saw this post... great news. My idle is erratic, but not all the time. Found and repaired 2 vacuum leaks, cleaned the throttle body and plate and the bore where the IAC seats itself (full of gunk). I adjusted the IAC pintle according to the Hayes manual but was getting a very high idle at first. Settled down a bit after 2 days driving back and forth to work, but still not quite right

 

There is an idle learn procedure that can be done to hasten a better idle. Note that daily driving will also cause the idle to be learned. It just takes longer and the idle can surge and the engine stall in the mean time.

Here is a link to a post I made on how to do the idle learn:

https://www.thirdgen.org/forums/v6/1...procedure.html

It needs to be done whenever the ECM is reset (such as disconnecting the battery). Or whenever the IAC has been changed or cleaned.

RBob.

 

Very cool, THANKYOU