So, i recently purchased a 2004 subaru liberty GT. the second one i have owned. the only modifications the car has are a AVO catback exhaust. i was told that it had been "tuned" however there is no paperwork and have no idea.
the problem i am running into is that at low rpm (1250-2500rpms) i have lots of shuddering, jerking, hesitation etc. The higher the gear the worse it is, and the more load the car is under inside that rev range the worse it is. once boost hits ~2500 to 3000 rpm it drives extremely smoothly with no faults. On idle it seems to be a little rough and almost sounds like it doesnt have equal length header.
i have replaced the spark plugs, cleaned all the grounds and the coil packs, used some upper cylinder cleaner in the intake manifold and ive still had no luck. fuel economy seems to be fine and nothing out of the ordinary, roughly 450 - 500 kms to a tank of 98 (mostly city and some highway).
I have no idea whats going on and ive been scouring forums trying to find a solution.
if someone could PLEASE help me i would appreciate it greatly.