Agreed. Almost never, ever a reason to touch that screw. That's why the factory hid it behind a plug that was not meant to be removed.Fix what's wrong before you go dorking with the adjustment screws. Sure, you can tweak an adjustment to hide the real issue, but if you ever want it to run factory-perfect again, don't.
X2 on what these guys are saying. JUST CLEAN YOUR THROTTLE BODY FIRST. This is normal PM maintenance anyway. Even if it isn’t your problem, it will give you a place to start. I have seen a few trucks with the exact same problem you have and they were all fixed with a simple spray down of the throttle body. You will use about 25% of the can so you will still have enough left over to do it a couple more times.Agreed. Almost never, ever a reason to touch that screw. That's why the factory hid it behind a plug that was not meant to be removed.
Yes, that's why you set the base idle with IAC closed. GM did it with the bone stock engine but, if you add any goodies, it needs to be done again. But, as I said in post #4 the OP needs to look at the throttle shaft for slop/wear which can also cause it to jamb under vacuum.That screw though, should be in contact with the throttle mechanism (zero clearance) - and be the absolute stop for the butterfly?