92 Galant Acceleration problems

I have a 1992 mitshubishi galant 1.8. Its having problems accelerating. When i push down the throttle hard it seems as if the engine is choking and doesnt accelerate at all, or very slowly. It works ok if i dont push it down only half way. Also it sometimes seems to backfire (in the exhaust??). I replaced the air-filter, so that is not the problem. It also has a new ECU. Does anyone know what might be causing this??

Check your Mass Airflow Sensor (a.k.a. MAS, or MAF). They go bad and may cause such symptoms. Best!