trying to troubleshoot an annoying stumble going from idle to gear and am wondering if my iac is the culprit. i have heard people talking about cleaning them and turning the "key"? i understand the iac's basic purpose and what it does but i'm just not really sure exactly how it works and what's involved in cleaning and/or replacing it. has anybody seen any articles that describe this process in detail?

im not sure how fast the iac is supposed to be able make adjustments, but it just feels like that when i put it in gear, maybe it stumbles because the iac isn't able to react fast enough? once it stumbles and i give it a couple seconds to recover, it idles just fine. i just want to make sure this is normal and isn't something i can overcome before i learn to live with it. i feel i have WAY too mild of a cam for a 383 to be having this kind of drivabilty issue.

thanks in advance!

 

Cleaning the IAC and passages is pretty basic. You take the bottom plate off the TB, remove IAC and clean everything you can get to. You don't manipulate the pintle of the IAC while it is out to keep from damaging it.

If the IAC is working properly, I would say your lack of idle control may have to do with programming for your modded engine.

 

Scan your PCM and see if it's pulling timing. I had a stumbling problem and found out that my knock sensor was going bad. PCM was pulling up to 12* whenever I pushed the clutch in. It got to the point where it would die every time I stopped. I know this is a bit different, but it's worth a shot.

 

so the iac unit and all of it's parts are in that plate that hooks to the bottom of the TB, or are there other parts that i gain access to once i remove that plate? also, i hate to be ignorant shoe...but what exactly is the "pintle" of the iac?

also, as far as the knock sensor, i have been using an LT4 knock sensor for a number of years, even before the 383 rebuilt. i did try putting my old stock LT1 knock sensor back in just to see what happened and it didn't help the stumble. do you think that was a good enough test or should i still try a new one?

 

You mean the knock module.
I'm typing about the knock sensor located on the pass. side of the block.

 

The pintle is the part you see that moves in and out to control the amount of air.

 

Try your stock MAF the Granatelli is known to cause drivability issues such as this.

 

96capricemgr....

I tried my stock MAF today for the first time but it didn't help the stumble. It was something I should have tested a long time ago though. Thanks for the suggestion. If you have any more, please let me know.

Robert

 

This is not the most popular modification but since you've modified everything else already, this is cake and could potentially fix your problem.

First however you need to get some scanning software like Datamaster to see if the IAC is maxing out. It does control the amount of air that enters the motor at idle but can only go so far and 160 is the end of its operating range. Now with that said... heres what I did to solve a similar problem.

Assuming you have a stock throttle body, you need to take it off. Right below the centerline of the TB is a small hole that bleeds air into the IAC passage in the intake. Its basically a bypass hole.. bypassing the IAC motor. If you simply enlarge that hole, it will help the IAC out by moving air it doesnt have to adjust for. The size of the hole depends on the needs of the motor so id suggest experimenting and of course starting with small increments till the problem goes away. IF the IAC is maxing out.

 

turbo....

actually, i had access to a Tech II scanner at a chevy dealership a while back when i was trying to solve this problem and the IAC counts were at about 46 sitting there warmed up in closed loop. from what i gathered on the forums, that was a pretty normal number so i sort of moved on. i read a couple posts from people whose IAC counts were maxed out at 160 just like you are saying, but i guess since that's not the case on mine, i shouldn't try drilling out the IAC passage?

i was talking to my mechanic again today about the stumble and he seems to think it's simple the difference in vacuum that's causing it and the stumble is just the time it takes to make the adjustment, etc. i guess i just find it hard to believe that's case since i went so mild on my cam specs for a 383 (218/224). i could understand it if i had gone a lot more aggresive.

robert