with a aftermarket maf? if so either get it replaced, or best bet is to get a used one from a junk yard, they run around 40 bucks and have a 60 day warranty. my jy maf is 4 years old now. best 40 i ever spent.
i think whats happening is it runs fine cold in closed loop, ( runs off the pcm) once warm its in open loop running off the sensors. and the maf is crappy causing it to run badly.