I have an 89 Trans Am with a newly built 383 with Vortec heads, HOT cam, SDPC intake and stock runners and plenum. When the car gets warmed up, it lopes the idle really badly from 400-1,600 rpm. I have replaced the module, coil and tested a spare IAC and nothing helps. If i disconnect the brown and black distributor wire I can get the car to run. If I have the wire connected, the lowest idle I can get is about 1,300 because I have to turn the idle screw out until the car smooths the idle , and this at 1,300. Someone please help me, I am at my wits end.

 

Ok, unplug your IAC. Your EPROM will not support such a radical setup. After you unplug your IAC motor, crank those throttle blades back closed until it will stay idleing in gear. In fact give it a few cranks more. I would say that you should idle around 750-850 in gear off the throttle blades and a little over 1100 in P/N. This is ONLY a temporary fix for you though. You need to get a chip burned for this.

Also, you are gonna want to reset your TPS. You grab a voltmeter and 2 pieces of copper wire, real this stuff, and then shove them in the top 2 positions on the TPS. You then take a reading after the car will idle nicely, you then loosen the screws and turn the whole sensor until it reads .54V while idleing. mmmmk? Should work for you for now. If not... I tried.

 

Isn't disconnecting the IAC gonna throw a code for him?

I've never heard of anyone just disconnecting their IAC . . .

 

No, it won't do any harm, but he does need to follow the minimum air proceedure and not just disconnect it.

 

resetting the Iac isn't doing it for me. It does not help the problem. I am gonna try and buy a new IAC today.