Why is my car failing to throttle and backfires ?

The crankshaft censor, the mass airflow censor, oxygen censor, throttle position censor, knock censor and the coil of my Subaru Forester Turbo 2 L 2002 has been changed but it does not take throttle and misfires. At times the engine works good but still does not want to take the throttle and when I raise the engine it back fires. It seems to be a technical problem because the check engine light does not come on again.