I'm a little confused on this one. It looks like my idle surge has been caused by a bad IAC. I disconnected it yesterday and it's been idling perfectly since then. The weird part of it is that I have no SES light and no codes pending. The car is OBDII and I know there are code sets that involve the IAC, so what's the story? Anyone else pulled the connector off and not thrown a code?

 

There is no direct code for the IAC itself. There are codes for low or high idle speed, but they are set by the difference between programmed idle speed and actual idle speed, not the IAC circuit. There's also a code that appears to be set by the IAC circuit (P1508) but that one is also based on both idle speed, and changes in air flow. It only runs the intrusive air flow test, where it ramps up the IAC and looks for increased air flow, AFTER the system fails the passive test, which it simply comparing actual idle speed to programmed idle speed (difference greater than 88 rpm). If your idle isn't 88rpm below the programmed value, its not going to test the IAC valve itself.

 

Well that explains it. It must just be dumb luck that it's stayed within the parameters then... Hopefully when I put the new one in the surge won't come back.

 

I unplugged mine and didn't get a code for over a day.