i have a 1993 manual toyota pickup with the 3vze engine (3.0 liter v6 with electronic fuel injection)
the truck runs fine but idles rough and stalls when warm. after starting, the truck idles around 1500 rpms, but once warm it can idle as low as 250 rpms. after the engine has been run hard (highway speed) the truck will stall when not in gear (in neutral or with clutch in).
adjusting the idle screw on the throttle body does not help

the spark plugs, wires, fuel filter, air filter, and oil filter have been replaced
the throttle body has been cleaned

any ideas?

 

One thing to rule out; back the whole idle screw out and look at the o-ring, they can get brittle and deteriorate to the point they don't seal anymore.

 

Where is the timing (ignition) set?