1996 Subaru Legacy 2.2 liter hesitates below 2000 RPM, idle

The car was running fine before my trip, the car sat for about 30 days. At first was very hard to start, used some cleaner in the throttle body, will start but idles at 500 RPM then will die after a few minutes, adjusted throttle postioner to get 750 RPM but that didn't help, engine still dies, so moved back to marked position. Looked around and saw the mass air body was cracked on top so changed it out with one I picked up at the junk yard. Still have idling problem, if I rev engine to 3000 RPM I can drive car to 70 + mph but once RPM drop below 2000-2500 rpm thee engine is sluggish if I push the accelerator to the floor at the lower RPM sometimes the engine dies.