tom3

I put the car back on the road a couple weeks ago, after months of sitting in the backyard.

Now, when the car goes from 1500+ rpm back to idle, it sometimes either dies or idles as if it was running on 3 cylinders.
The scanner indicates a count of 50 during the normal idle; but when it idles weird, the count is 0. When this happens, if I rev the engine and let it go back to idle, it may either die, stay at 0 and try to idle or it will go back to 50 and idle normally.

This can happen anytime, cold or warm.

So, my question is: what could cause an IAC count of 0 sometimes?

Injuneer

What you see on the scanner is the position the PCM is telling the IAC motor/valve to take. There is no feedback to tell the PCM whether the IAC motor is actually working, or what position it is in. The PCM is seeing the higher than spec idle, and trying to close down the IAC valve to reduce it. But apparently the IAC motor is not responding. Or, there is an intermittent vaccum leak that is allowing the air to enter the intake manifold without passing through the IAC system.

tom3

Maybe my first step will be to clean the IAC and see what happens; otherwise I'll hunt for leaks... if it's intermittent, I can only think it's in the rubber parts.

How's the IAC controlled? is it through current, voltage or pulses?

Injuneer

Its a "stepper" motor. The PCM moves it in and out with pulses.

tom3

ok, cool;
I'll investigate if it is dirty or stuck.

What is really odd is when it is 0 and idles like crap, I can turn the car off, then on and it's back normal right away. Also, reving will sometime make it work right again.
If the car dies, I can just start it and it'll work properly again...

I'll post again after the cleanup!