My 2.8TBI engine runs fine on the highway but wants to stall at idle .When I run the scan tool on it the O2 sensor shows rich at idle .The idle is about 900 rpm and will cut in and out almost like turning the engine off just for a second.
Any ideas ?

 

It scarb'd correct?
Could be as simple as a minor adjustment.
Although to be honest, its been 20 som years since I messed with a carb in a truck.

 

nope not a carb engine it is a TBI engine.

 

I would start with checking the fuel injectors...take off the air cleaner and see if theres any dripping from them at idle. Also check your EGR valve, if it's got any carbon build-up on the pintle that would cause it not to close off and to run rough at an idle. Last but not least check the IAC ( idle air control valve) This is what controls the idle speed, not sure how to diagnose it without changing it out though, maybe someone else here knows how.