1999 Subaru WRX • 4 cylinder AWD Manual • 144,000 miles

1999 Subaru Wrx,
my car tends to run rough and has a flat spot at low rpm's that is getting worse the more I drive. Also I replaced the leads, spark plugs and fuel injectors, I was also told it was my airflow meter my be the problem, which I replaced but did not fix the problem, do you have any ideas on what it could be?
Lawrence 2011
January 27, 2011.

Could be caused by one of the following below

Oxygen sensor.
Catalytic converter.
Fuel injectors dirty/sticking.
Mass airflow sensor/Airflow meter.
Throttle position sensor.
Crankshaft position sensor
Knock sensor
Manifold absolute pressure sensor.
EGR Valve
Fuel pressure regulator leaking 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 it and keep testing.

Jan 27, 2011.