idle "stuff" continues....replaced IAC.....now Knock Sensor code AND......

[rrs814]

Replaced IACl (had it done, I'm incapable)..... AND now...... when started cold, idle goes to 2,000 up and down irratically to 1200, then 1800, then up/down-back/forth for a few minutes, even once warm. Once "settled" (warmed about 4 "notches") to around 1100, put in gear then it goes down to about 7-800 and behaves nearly normal. Knock sensor code now appears as well. ANY THOUGHTS???? PLEASE...before I take it back in. THANKS!!!!!!!!!

[Ronnie]

What were your symptoms that led to changing the IAC?

Do you know if the mechanic cleaned the cavity where the IAC pintle seats? That is very important to operation of the IAC.

Cleaning the IAC (3800) - Reatta Owners Journal

[rrs814]

1990 engine rebuilt about 4000 m ago. Idle speed occasionally will go up to 12 or 15 while sitting (in OR out of Drive). Sometimes will fall back soon, sometimes not at all. Oddly, when the "old school brain" kicks in, I'll hit the pedal, and it will usually fall down to normal. -------------------- see below ------------

ORIG POST - http://forums.aaca.org/f116/idle-speed-gremlin-up-then-down-335326.html

[Guest crazytrain2]

You could try disconnecting the battery (neg) wait about ten minutes or so then reconnect. This will clear the old settings from the memory.

[Don B.]

The throttle position sensor can cause odd idle issues.

Sometimes if you wiggle on the connector, if the sensor is bad, the idle will change maybe even stall.

[Guest MercWagn]

The throttle position sensor can cause odd idle issues.

Sometimes if you wiggle on the connector, if the sensor is bad, the idle will change maybe even stall.

Agree with Don. Recently diagnosed an idle issue on a different GM application, turned out the TPS was the problem, even though it didn't trip a code. You can access this info through the on-board diagnostic-ED01, idle voltage should be around .33 to .46 ( set my initial to .38). Voltage should increase as the pedal is depressed--check connector also. Might also want to check ED04, as incorrect temp sensor readings can cause the ECM to do some odd things with idle.

Of course, there may be another problem, but it is probably jumping the gun a bit, given more tests need performed, but a bad ECM could likely create this problem as well.

Good luck.