(08-26-2024, 10:21 PM)Keith1976 Wrote: Hey man , start by engine cold does it do it or when it's hot . You can rule out if it's an open or closed loop by timing . Also if it's an injector she would be smelling like fuel and unstable idle and hear it in the exhaust tone . So many things can cause this . I'd check all vacuum lines especially the line to the transmission regulator . U can get one of those nipple plugs cheap at the part store to rule that out . Pull the line off the upper  intake manifold it's by the pvc valve and cap it start up and see . Also there is a u tube video about gm fuel injectors by tapping them with a 3/8 extension and back edge of a screw driver to se rig the engine stumbles as carbon is built up . Being the Iac is giving you an issue could be carbon built up inside where it sits in the throttle body or the throttle plate having carbon build up as well . I find once a year the throttle body comes off and I clean it . So I would do things in small steps before throwing parts at it . If no check engine leak then simple things . About the open closed loop could be as simple as a coolant temp sensor or a o2 sensor out of specs causing it to run rich and having idle issues . Mx67627@aol.com sir as always send a email