Subaru Repair: Misfire, loss of power & engine judder, throttle position sensor, wastegate actuator

Question
I was wondering if you could help. I have GC8 Impreza turbo -1999. It suffers badly from a sluggish power drop at below boost levels, occaisonally misfiring until it comes on boost! It then accelerrates in a stop-start fashion, almost as though the handbrake is being pulsed on & off! I've so far replaced coilpack, plugs, plug wires, boost solenoid, wastegate actuator, all boost pipes renewed & most recently the fuel filter(engine bay). What else do you think could be causing this problem?  ...help...

Answer
Have you checked fuel pressure, and exhaust back pressure?
That is where i would start.Next i would do a throttle position sensor sweep test to make sure it doesn't have a dead spot.Check those things and let me know if i can help further

Justin
All Wheel Drive Auto