Stumble at idle

[Prospeeder]

Well my 3.1 in my 1990 6000 has a pretty unstable idle, It will drop abit every so many revolutions like it stumbles. It revs smooth and pulls hard with pretty good mileage. The Plugs and wires are new. The EGR looks like its pretty new also. I dont think theres any vacuum leaks.

[dcjredline]

Idle Air control valve, Computer, and MAP would be my 3 guesses.

[Jr's3800]

Idle Air control valve, Computer, and MAP would be my 3 guesses.

I agree...

First thing I would do is yank the IAC and clean the IAC channel and IAC Tip.. Disconnect the Battery to blank the computer.. Might take you feathering the throttle to get the car to idle.... Once the car warms up take it for a spin and get above 40 mph, this will allow the ECM to relearn the IAC..

Is this car storing any codes at all?

[TheGutlassCutlass]

In my opinion, this has ALWAYS been an oxygen sensor issue with the 3.1L V6. If your idle is not lumpy when the motor is cold, but it is when warm, it's the 02 sensor.

[crabhab]

My 1994 Ciera Wagon has a rough Idle that smooths out with engine speed. I hve no CEL light and I am getting about 26mpg. I have bought a Factory Service manual off of ebay. I have replaced pcv, air filter, oil and filter and I want to replace plugs & wires, fuel filter, and clean IAC motor.

Is it hard to clean out the IAC?

Thanks

[dcjredline]

No its not hard. Do a search online for it and there are instructions available.

[Jr's3800]

In my opinion, this has ALWAYS been an oxygen sensor issue with the 3.1L V6. If your idle is not lumpy when the motor is cold, but it is when warm, it's the 02 sensor.



First while that is possible, I would not Doom the O2 unless you have watched the both the O2 toggle and Voltage along with the Swing or Cross counts...

And what ever direction you go in, Most GM's don't do too well with a Bosch O2... I'd use either an AC Delco or Denso sensor..

If prospeeder has access to a scan tool, I would take a close look at the TPS, O2, ECT, MAP to get a good idea of what the sensors are doing... As well look at where the IAC is as compared to what the ECM wants it to be... Same goes for the idle, Look at the actual idle RPM compared to what the ECM is trying to command... Should be pretty close, give or take 50-75 Rpms:)

[dcjredline]

First while that is possible, I would not Doom the O2 unless you have watched the both the O2 toggle and Voltage along with the Swing or Cross counts...

And what ever direction you go in, Most GM's don't do too well with a Bosch O2... I'd use either an AC Delco or Denso sensor..

If prospeeder has access to a scan tool, I would take a close look at the TPS, O2, ECT, MAP to get a good idea of what the sensors are doing... As well look at where the IAC is as compared to what the ECM wants it to be... Same goes for the idle, Look at the actual idle RPM compared to what the ECM is trying to command... Should be pretty close, give or take 50-75 Rpms:)

Yeah since I said my peace in the other thread I decided not to here cause I didnt want to seem like I was PICKING on anyone.

I agree with Jr on this completely!!!