Crossfire Idle Gone Mad

[JohnGrawcock]

The idle on my 82 coupe is out of control. When I start the car the idle goes to 3000 or 4000 and ramps up until I turn the key off. I'm hoping someone will have a suggestion to help solve this problem. I've done the following:

- Verified that the throttle plates on both TBI units are fully closed
- Verified that no trouble codes are set (reads only 12)
- Verified that there are no vacuum leaks
- Checked operation of EGR valve
- Verified adjustment of TPS
- Unplugged both idle air motors. Idle did not change.
- Replaced gaskets for both trottle bodies and the upper plate of intake manifold as suggested by GM service bulletin.

The only thing I've found that brings the idle down is blocking the air intake ports at the top of the throttle bodies above the idle air motors. This makes me think that the motors are not restricting the air flow enough to control the idle. The fact that both units behave the same makes me suspect the controlling signal rather than the motors. Does anyone have any suggestions or the information necessary to debug the IAC circuit?

 

[82X-FireVette]

It sounds as though your IAC motors are not working correctly. Make sure the ground straps and wires have good connections. You should be able to see the pintles inside the air passages with the engine off as they are normally closed. If you have no stored codes, the computer must be working OK. You can test the IAC motors by removing them from the TB's and following the procedure in the service manual. I can give you the procedure, if you don't have the manual. Make sure you retract them before reinstalling so you don't damage the TB's. They retract when the computer is put in diagnostic mode. Then you disconnect the wire connectors from them to keep them retracted. I had to replace one IAC motor. It was working intermittently, causing huge idle fluctuations.

 

[JohnGrawcock]

82X-FireVette,

The manual I have does not give a proc. for testing the IAC motors. I also have no pinout for the connector. If you could post it that would be great.
However, I still suspect that the proper signal is not getting to the motors. It would be strang for them both to fail at once. Do you have a pinout for the ECM connectors? I want to verify continuity of the wires from the ECM out to the IAC motor connectors.

Thanks for the info,
John G.

 

[82X-FireVette]

John,

I have attached the diagnostic procedure for testing the IAC motors. I hope this helps.

Bob

 

[82X-FireVette]

John,

I have attached the ECU connector diagram that includes the ALCL pin layout. You will need that to do the diagnostic.

Bob