Ok, I've got a scanner and was watching it while my car sparatically was idling on it's own reving up. The TPS is good staying at .63 or .65 volts with no throttle applied and increasing slightly as more throttle applied. IAC was fluxuating greatly I believe the lowest position I saw was around 10 or in the teens and all the way up to 140 or so. This is all while the engine was idling in park or drive but no throttle applied only brake. Is this a sign of a bad IAC valve? I checked the resistance on the valve and it appeared to be 54 ohms which should be good. Could the PCM be giving it a wrong signal for it to be changing it's position like this or is it the valve itself. I cannot find anything that says what the position should be at idle and I'm guessing it shouldn't fluxuate like I am seeing while idling. Please help me with the right answer or I'm gonna have to kill something like my car...

 

5- 50, normally around 35 or so I guess. It depends on the idle requirements for the car at any specific time. Check for vacuum leaks.

 

In the ballpark of 30-40.

 

~20-40 on a warmed up, stock engine and stay steady. It should not swing wildly at idle. With engine cold, it will be higher, but slowly come down as the engine warms. You probably have some other problem that is causing the IAC to swing.

 

You might want to read this.

And to clarify further, the scanner is reading the number of steps the PCM is commanding the IAC motor to open. There is no feedback on actual position.

 

So a bad IAC would not cause this to happen? Is it the PCM sending these signals and coming from somewhere else? and where? I've checked for vacuum leaks several times, not found any. The wierd thing is I'll hear a psst and then it will rev up like the fuel injectors are giving more fuel. I also disconneted the wire going to the TPS while running and while it was unplugged it didn't rev up. Just some more info if you have any more insights

 

i have the same problem on a 94 a4 its driving me nuts . have checked for leaks new egr and intake gaskets what could be wrong or what could i be doing wrong . getting ready to torch the f$%ker

 

I guess it might help to look at the input factors that affect the IAC count. Things such as MAP, MAF, ECT and anything else. Maybe your MAF is dirty.

 

I discovered that my throttle blades were slightly open as a result of some mechanic previously trying to adjust the idle by turning the throttle return stop screw on the throttle body. with the throttle body removed i held it up to day light and could drive a bus in the gap between throttle blades and the throttle body bore . After backing the screw off i noticed a very small gap between the blades and the throttle body bore. I refitted the throttle body and after warm up the car idles with the iac at 20 steps she also idles much lower now on cold startup and the iac once showed a reading of 16 steps . There is still the occasional slight rev to +/- 900 rpm (from idle at 675rpm) could this be as a result of the small gap between the throttle body bore and the throttle blades. Should i replace the throttle body.