deadbee

I have a 1995 wrx import, manual , and have a few problems with flat spots etc. Replaced the coil packs and the problem seamed to go away.
Car seems extremely heavy on fuel even when driven gently. Noticed when pulling away from standing start when driven hard, when changing gear it's as if the clutch is slipping but its not(revs dont increase),when you back off just a little the power comes in and if fed in a little gentlyer it pulls ok. But now the car is knocking really loudly at 3000 rpm sounding like a big end.(so my mechanic says)
please any advice, what is maf sensor? Can this cause this failure.

Managed to locate another engine but it has a torque converter is this the same engine as a manual?