V6 2.8L
That TORX screw definitely DOES affect idle. It seems odd, considering the function of the Idle Air Control. How is it properly set?

Thanks!

I won't go into detail on how to adjust these. I would need to pull out some old lit to do so. There are many here that have recently looked it up and will mosy likely respond.

With that said. If it has not been messed with don't screw with it. It is not a idle stop, It is a Throttle blade stop. Because throttle bodies and blades will always have slight differences, this screw is set when the throttle body is manufactured. It is just to keep the blade from binding in the bore. Very early fuel injection systems would use this as a minimum idle air screw. That was before stepper motor idle air control motors were used. Those systems used solenoid type idle controls and were very unreliable. Case in point was the early Caddy fuel injection they used on Olds 350 engines. Anyone who worked on them would remember how bad the cold idle control was. Early Japanese L jetronic used 2 screws(one was capped off) one for the blade stop and the other was a minimum idle air setting.
Without going into a manual I can tell you if you have a TPS lever that has not been bent, you need to have the blade stop set with the TPS voltage under .5 volt. More will normally cause a TPS code. And having too much air pass the blade will cause a IAC code. These due to the ECM not being able to reduce idle by closing the IAC or TPS voltage not returning to an idle reading. If I set these and don't have the specs, I set it as close to fully closed as I can without the throttle blade binding in the bore and I do this with the engine off. I can tell you I have not had to set one unless someone has screwed with it. If you are having an idle problem you need to put it back and look for another problem. One very common problem with bumping up this screw is when it is set too high the ECM sees too much TPS voltage and doesn't try to control idle anymore by running the IAC motor in. Errors with the TPS will also cause the ECM to drive the IAC in and cause the engine to stall.
If you are changing your idle through this screw, you are treating the symptom and not the problem.

[This message has been edited by cmechmann (edited 04-19-2014).]

You can adjust it a couple different ways.
1. Using winaldl, or equivalent, adjust it until the iac steps to around 20-30.
2. Jumper a and b on diagnostic terminal, key on don't start. Wait 30secs, then disconnect iac connector. Remove jumper, then start engine and adjust idle to around 900. Shut off and reconnect iac.

In either case, you may have to set tps to 0% winaldl or around .47volts because you've moved the throttle plate idle position.

These adjustments should not be necessary if no major work has been performed......in a perfect world.
Cleaning the crap out of the iac passages and performing a sea foam Chinese water torture should be performed before messing with the idle.

Did a little reading (not from GM) but from from a few tuner sites. You will need something to block the IAC passage, set the ECM in service mode, and set idle 100 rpm under what minimum idle control would be warm by what the prom displays as minimum.
example: If connected to a scanner and minimum idle displayed is 600. Different prom will have different minimum idle. Block passage or close IAC and disconnect(so no air passes) with ECM in service mode through scanner or jumping aldl connector and set screw to 500 rpm. Then adjust TPS voltage to idle spec. .45-.55v Reconnect IAC, reset ECM.
But this was also for a 1989 2.8 in a different car.

properly set/reset idle stop is See my Cave, Idle Stop

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