This is sort of anecdotal and also to see if you have seen these same symptoms with a bad IAC.

I just finished my heads/cam/intake/LS6 pcv system/oilpump/chain/PS pump/paint exhaust/move tranny temp sensor from cooler line to tranny case/AMW can/plugs/fuel filter Marathon Install

and everything is perfect except the idle likes to be 3500. sometimes 2500, etc. I know some people (including myself) have seen cases where after the battery has been disconnected for a while the idle will be way high and it takes a couple of re-starts or some idle time for it to come back to normal. It never came back in this case after maybe 10 different starts.

Unplugging the IAC has no effect.

If you remove the IAC and push gently on the pintle with your finger it _will not_ move back like it should.

Cleaning with brake cleaner and lubing with 3 n 1 has no effect.

About 1 second after motor stops completely at shutoff I suddenly hear this awful 'marbles-in-a-can' sound coming from the IAC...which I assume is the IAC trying to park itself and stripping the teeth on the worm drive inside.

Oh well, one more R&R in this install

 

I don't think it should make that noise, so it is probably bad. You may also want to look for vacuum leaks.

 

That much rpm you sure you dont have a vacuum leak? Remove EGR something's got a huge leak. That is a little out of the IAC's possible window to allow 3K in RPM.

 

The IAC can go up to that range. I know this from some experiments in another time:
http://members.fbody.com/RCowan99SSConv/stepper.html


I would swap with a friend but I don't know any LS1s here yet. I'm getting another one today.

 

I have a cool idea. Plug the IAC hole up with chewing gum and see if your idle goes down!

Or you could just use your hand or something.

At least then you will know if it is a vacuum leak or the IAC!

 

Well I know its bad because I took it out and its locked up, you can't unscrew it or push it in. I'm pretty sure the source of the failure is a heavy dose of brake cleaner when I left it in when I cleaned the TB. DOH!

There are some excellent, simple, ubiquitous tools in this world like brake cleaner, duct tape, rubber bands, surgical tubing, and breaker bars.. but sometimes they just aren't appropriate.

New one arrives tomorrow.. we'll see then. Thanks PACE!

 

Brake cleaner. That explains a lot.

 

You cannot push or unscrew the IAC motor. It is a electric worm drive motor, they only move with a power & a ground applied.

 

Sorry wrencher. Its an electric stepper motor with a worm gear, yes. And you can pull yours out and push it in by hand. Also the Helms manual says if the pintle falls off during handling you can screw it back on.

Also if you unplug it and run the car, the air can push it back raising your idle because there is no holding force in the motor with no power to it. There are more details about that stepper motor, operating voltage, current, bipolar, etc. from that link: http://members.fbody.com/RCowan99SSConv/stepper.html

 

The new IAC fixed it. Now its all over but the tuning.

 

I am going through exactly this, 2500-3500 rpm idle. I checked for vacuum leaks till I was blue in the face, all to no avail.
Upon pulling the IAC out, the pintle separated. I screwed it back in. I am going to go try it now. This is new. Delphi unit.
Result: That was the answer. I never expected a new part to fail like this.

 

ooooooo

 

You beat me to it.....

 

You owe me $10. Don't let it happen again or it'll be $20.

 

OK. Put it on my tab.... lol