I was having an occassional code 35 and the engine searching for idle over the last couple of months. Not very often just enough to be annoying. Then, I did a complete rearend tear down, pulled the tank, changed the fuel pump, in tank filter, pulsator, and hoses. The tank is back in and hooked up for testing before putting the diff back in.. The car started, idled high, searched, run rough, idle really slow and rough, then die.. Check of the fuel pressure shows a solid 38 to 40 continuously while it runs.. No change to fuel pressure when it dies suddenly.. Changed the IAC, same problem except with the old one it would run rough for a while then die.. With the new one it just dies outright when I let off of the gas.. Fuel pressure all normal.. Other new stuff in the last 8 months.. New fuel filter, new FPR, and rebuild and cleaning of injectors.

Any thoughts? Does the IAC have a relay or is it just driven directly off the computer?

Thanks...

 

Did you clean out the IAC passages in the throttle body?

 

Yup, cleaned them before the new one went in..

 

Pull your battery terminal and do an idle relearn.


Posted from Thirdgen.org App for Android

 

Already did that.. Pulled the cable after I installed the new IAC and then started it a couple of times..

 

How many miles on the engine? Does the engine have the original Multi-Tech injectors?

 

IAC length to be 1 1/8" ... gasket to end of pintle.

Otherwise, here is the info from the tech board.


Tom Keliher Mar 31 2006 - 4:07pm
Idle Air Control


Tools needed:

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2. [*]
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Take the paper clip and open it up and form it into a big "U" shape. Insert the clip ends into the ALDL in the 'A' and 'B' pins.
Turn on the ignition, but don't start the engine. Wait 30 seconds. Now, go remove the connector from the IAC.
Start engine. You are now going to adjust "minimum air". There is a Torx screw on the side of the throttle body. This is what needs to be turned to adjust minimum air, or more commonly known as "idle speed". It comes from the factory with a protective metal cap over it. If the cap is still there, use a small punch to knock it out. Set the idle speed to 450 rpm, rotating the Torx screw clockwise to raise rpm, and counter-clockwise to lower rpm. Once the idle rpm is set, turn off the engine.
Re-connect the connector onto the IAC. Start engine. Idle speed is now once again governed by the ECM, but your idle should be smooth and steady, approximately 600 rpm in Drive (for unmodified cars).
If you set an SES light by having the IAC disconnected, then after shutting down the engine disconnect the negative battery terminal. Wait 5 minutes. This will clear the ECM of all trouble codes. Re-connect the battery and drive the car for 20 minutes to allow the ECM to relearn your driving style.

 

Thanks for the input.. The new one came apart as I took it back off.. The pintle actually stuck in the intake port.. I tried it outside the port and it blew the pintle out the end again. So, its going back.. I did some more cleaning on the old one including using a wire brush on a drill to "polish" the end of the pintle and it is working much better now.. My guess is that there is really something wrong with the new one or that it is just plain wrong for the 3.1L...

 

Thanks for the post. Guess I need to pull off the new IAC I put on today and check the length. I don't have the same problem as LarryD. My car was burbling & felt like it was backfiring when starting to press throttle. Also idle would often stay high when I pressed the clutch coasting to a stop light and then gradually drop down to near normal.

Replacing the IAC made the car run better, but still getting a bit of burbling & back fire like behavior. Hope adjusting the IAC solves my problem.

 

Back fire'g like symptoms would look at timing adjustment.

 

Thanks. I've adjusted the timing several times and currently have it advanced 10 degrees. Doesn't seem to make much difference wherever I set the timing.

Adjusted the IAC and cleaned up all the carbon. Also found part of the gasket on the top plate missing along with loose star bolts. Hopefully that solves the problem.

If not, there is a GM bulletin on 91-92 3.1 sagging that describes the procedure for solving. Guess that will be my next step.