1996 Subaru Legacy

Engine Performance problem
1996 Subaru Legacy 4 cyl All Wheel Drive Manual 248000 miles

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.
June 9, 2010.

Inspect and test all the following listed below: Oxygen sensor.
Catalytic converter.
Fuel injectors dirty/sticking.
Mass airflow sensor/Airflow meter.
Throttle position sensor.
Manifold absolute pressure sensor.
EGR Valve
Fuel pressure regulator leaking, fuel filter clogged or defective fuel pump.
False air leakage.
Fuel contamination.
Foul/defective spark plugs.
Open spark plug wires.
Ignition coil/Coil packs defective.
Incorrect ignition timing.
Cap and rotor.

Note: If it doesn't apply disregard.

Jun 9, 2010.