IAC symptoms


Active Member
Dec 18, 2009
Do the IAC sensor on our cars go bad ,if so what are the symptoms.Last week I checked my IAC reading on my ScanMaster and it was at 33 so I decided to adjust it down to 15(TT chip recommends between 10-30) .After every adjustment on what looks like a idle adjustment screw I shut the car off so the IAC can reset then started it up to see where it settled.After I got it down to 15 I readjusted my TPS at idle .42,wot 4.48,I did this with engine warm in park.I then took it for a 10 mile cruise and rechecked the IAC and TPS,then after I did a wot 3rd gear blast I rechecked IAC and it was oscillating from 50-54 then it settled at 51.After letting the car sit for about 30-40 minutes I then restarted the car got it up to temperature and the IAC in park was at 15,why is it changing so much?Am I doing something wrong? Thanks,ikle.
It sounds like you adjusted the IAC correctly and it is working properly.

The IAC count is not a static number but rather one that goes up and down all the time. The IAC motor is the only way the computer can control the idle rpm. Basically, when the actual rpm does not match the target (programmed) rpm the ecm adds or subtracts to the IAC count. This lets more or less air into the throttle body which changes the rpm to be closer to the target. Since the actual rpm varies up and down, the IAC count should change to constantly make adjustments.

Many things affect the IAC count at any given time with the most critical being the adjustment, how clean it is, the coolant temperature, and throttle position. If you adjust it to 15 at idle and at a given temp. then it should always go to 15 or close to it at that same temp. With an idle count of 15, you would see a count of 55 while driving or when the throttle is pushed down.

Thanks for the reply Dennis,I did take the car out again(having boost issues:mad:)but after I did another run all the #'s looked good on my ScanMaster at idle and the IAC was at 17.I thought I was adjusting it right but I am new to these cars and wanted to make sure I am doing the right things.Thanks again,ikle.