I have a 7730 ECM with an automatic transmission.
I've verified that my IAC is functioning properly, but what is happening is this:


When I come to a stop, the engine doesn't want to idle down to the specified 650 rpm (especially after driving on the freeway). As a result, it downshifts quite hard. However, after stopping, I shift the trans in to neutral and the rpm jumps up to about 1300 rpm and then falls down to the 650 rpm after about two seconds. If I shift back into gear while stopped, it stays at the 650 rpm and idles nicely and constantly at that speed. When I get up to speed again and I come to another stop and it starts doing the same thing again.

Another thing I notice is that when I'm stuck in traffic, when I come down to about 5-10 mph and shift into neutral at that speed, the engine stays at 1300 rpm until I come to a complete stop. Shouldn't the engine just fall down to 650 rpm if it's not in gear?

Is there some other function in the calibration that relates engine rpm control to vehicle speed? I have the "minimum vehicle speed for idle" value set at 15 mph. So at 5-10 the ECM should consider my engine to be idling. Is it sometihing with the decel fuel c/o?

What gives?

 

How many miles are on the IAC? has it ever been cleaned?

I cleaned mine the way Vader describes in his post and it made a huge difference. There could be a bunch of carbon built up impeading its easy movement.

 

It has less than five thousand. I've also had it out a couple of times (and cleaned) during my search for that idle-misfire.

Since my cam, heads, exhaust, manifold, etc are all different from stock, something in the calibration needs to be changed.

 

Heres a good one u can try as a test ..

Pull out alkl your overrun timing and fuel(say 35ka down, wherever it is when your off the gas coming to a stop) until it starts to surge then back it up to where it no longer surges..

Once u get that worked out nicely u can slowly raise it until your brakes feel good when stopping(not sure how wild your cam is) but it helped me 0out a lot... U let off it wil drop like a rock :-)

Later
Jeremy

 

You might want to look at the table at location 86b2 called "IAC manual throttle follower vs. MPH". This one adds steps to the IAC position depending on speed. I had the same symptom and zeroed out the steps added up till 40 mph. Drives much better now.

Steve

 

Problem is, I'm running the CATS tuner which doesn't have that parameter. But in any case, another guy in another post of mine helped resolve the issue. It runs great now. Thanks though!