Idle problems

[HotRodPC]

Cool. That was easy enough. Noone here would have suggested that. Seems the very easy minor crap like that, we just assume is there and already been checked. Good News nonetheless !!!

 

[sticman]

I've noticed it does it just when the truck is warmed up. When it's cold it idles around 1000ish and it's fine. But when it's warm it goes down to 600 and idles out or does the pulsing thing where it goes up and down.

This is a basic statement of computer control. When the truck is cold, more to the fact the O2 sensor is cold. the truck runs at high idle to warn up the O2 sensor, aka Open loop. Simplest control, just the bare necessities to start just about any motor. When the O2 is warn and signaling, the computer switches over to Closed loop and monitors more sensor points on the motor. In the closed loop mode the computer is trying to correct for a problem, or corrects into a problem, thus the surging.

 

[HotRodPC]

This is a basic statement of computer control. When the truck is cold, more to the fact the O2 sensor is cold. the truck runs at high idle to warn up the O2 sensor, aka Open loop. Simplest control, just the bare necessities to start just about any motor. When the O2 is warn and signaling, the computer switches over to Closed loop and monitors more sensor points on the motor. In the closed loop mode the computer is trying to correct for a problem, or corrects into a problem, thus the surging.

Good info here stic !!! I've also been taught the same about Coolant temp and the Open and Closed Loop operation. That some computer systems will not get into Closed Loop operation til coolant temp is 190 degrees. Which I did always wonder if that wasn't maybe a 2nd stage because I know many vehicles actaully take a long time to reach 190 degrees. So it is possible that the GM C4 system, aka Computer Controlled Catalytic Converter which is GM's first PRODUCTION comptuer system or maybe even the CCC aka Computer Command Control, GM's 2nd PRODUCTION system uses also?

For many years now vehicles are computer controlled even when the motor is cold which is what increases efficientcy being that many trips in your vehicle are not even long enough to fully warm an engine. You go to the grocery a mile from your home, shut it off. Come out 10 minutes later and drive home a mile, your vehicle didn't even get to half of normal operating temp.

 

[chengny]

Start by checking the electrical connections at the TPS and the IAC. These two components are dependent on each other. Make sure the contacts with in the plugs are tight and free of oxidation.

Read this thread:

http://www.gmsquarebody.com/forum/showthread.php?t=4384