I had this very same problem, it turned out to be quite a few things:
MAF was really dirty
ISV was shot
Distributor timing was off (from what I've been told, this can happen pretty easily)
Harness connectors for MAF/ISV/TPS were corroded
Intake boot had a small tear
this is a really hard problem to figure out/solve because it could be so many things, or all of them working against you at once.