Carb. ?

[COBALT]

Did you just rebuild this thing, or has it been running ok before, but not so good now?

Before you start messing with the idle screw can the fast idle even be set correctly? You should be able to pump the accelerator once before firing up the truck when cold, and preset the butterfly. The idle screw should ride the stepped cam to force the linkage. If that's not happening then I'd say yes mess with the screw. If it is happening, then your preset idle needles at the base of the carb aren't set right, or your idle bleeds are clogged...