My ranger 4.0L V6 has been idling rough and dieing when stopped. it would clear up if i rev at about 1000rpm but wont idle itself. i was told it was upper manifold gasket so i replaced the set upper/lower/valve cover gasket since valve covers were leaking and intake was coated with gunk (crankcase vent hose had been off for few years apparently) i clean everything as best i could assembled and now its worse. IAC unit seems not to move ( i removed from intake engine revs high no movement in IAC with it mounted engine revs high IAC off/bypass hole blocked engine dies instantly thought i knew when i started now i have no clue any ideas would help greatly

I'd start with the IAC motor. Those are prone to failure.

i tested it and was within limits but i pulled it off and it doesn't move also it backfired a couple times and never did that before seems to be worse now that i replaced intake gaskets and cleaned everything

I had a similar problem as you with my Ranger. Twice now. Both of my IAC's were complete crap. The last one that went on me would cause the engine to idle according to the A/C. When the A/C cycled on, the engine would idle down. When the A/C cycled off, the engine idled up. There's really no good way to test an IAC, because they can either fail, or they can semi fail, as my last one did. If you have $45, go to Auto Zone and pick up a new IAC and swap it on. Drive it around for a few hours, let the truck learn it's idle strategies, and then see if that helps. If not, take the IAC back for a refund. This is the easiest way I found to figure it out. Chasing down vacuum leaks is a major pain, swapping the IAC to rule it out is a matter of two bolts, a connector, 5 minutes, and $45.

im pretty sure the mechanism inside the IAC is broke i see no movement in it when the truck is struggling to run i cleaned the throttle body and intake (it was caked with dirt) it wont run long enough to drive for computer to adjust settings and has backfired a few times now could i have done something to cause this what would cause backfiring