is it only on the throttle or is it in idle as well. It could have something to do with IAC being filled with carbon junk. Or your entire manifold even.
If you're playing with the intake and have it off. open the trottle body and look down. A friend of mine had a tahoe and it ran like crap and died because the tottle plate was blocked
Cleaned it out and the truck right 1000 times better (gee I wonder why)
Just some thoughts to take into consideration.
