My 91 chevy lumina 3.1 has developed an excessively high idle. I cleaned the IAC but it didn't really help. should i replace it or be checking something else. thank you in advance, Mike.

How high is the rpm at idle?
Before you replace the IAC with a Delco one ..have u scanned for an codes? any lights on?
I would also want to know if the throttle plate is clean and closing properly not sticking anywhere inside. Ensure throttle cable has smooth movement/operation.

Vac leak?

Had a similar problem on a 95 3.1, took it to dealer and they adj the IAC to lower idle. After that I realized it was something I could do my self.

once you clean the tb butterfly, iac, iac seat, then you can set it on obd1 by removing the battery cable for a while then reconnect it, and run it in drive at idle with the wheels blocked against something substantial.

Had a similar problem on a 95 3.1, took it to dealer and they adj the IAC to lower idle. After that I realized it was something I could do my self.


You can't adjust an IAC......it is just a motor, that is commanded by the ECM, to whatever position that is needed.....

What you can do, is clean the crap from you throttle body bore AND throttle body plate.......there is an adjustment screw to adjust the throttle plate, but rarely do you have to adjust it, if the throttle body is clean and your IAC is functioning.....

With a high idle, as has been mentioned, the throttle plate can be hanging open due to crud(or the swivel points are not moving freely), even crud on the IAC pintle.....could even have a kinked accel cable or cruise cable.....a vac leak is also another possible problem......

Most techs have an electronic tool where they can manually open and close the IAC to check it'* operation.....

Also, a scan tool is helpful.....looking at the IAC counts...normally, should be 10-15 counts at idle, normal operating temp, and no A/C on.....

If you see high counts, and idle is high, the computer is commanding the high idle for some reason.....if idle is high, and counts are zero, and the IAC is ok, then you obviously have a vac leak...

Thank you everyone. I will try cleaning everything and get back to you. thank you all.

After you clean everything, like JW suggested, you should do an "idle learn" procedure to prevent stalls.....

can you tell me the procedure of an "idle learn"? thanks!

see post 5