e46 n42, missfiring like a be-atch

hi guys, ill try keep this brief as it goes way back, id appreciate the 2mins itll take you to read it coz im at my witts end,

cars always idled poorly, so i have changed,

1 owner, full history 2003 39000.

bosche coils,
plugs,
entire ignition wiring loom,
o2 sensors,
cam sensors,
crank sensors,
temp sensors,
de sludge,
oil n filters about 6 times in a year.

that improved idle massivly, but at xmas it started missfiring like mad, so we unplugged maf, ran it for a hour or so, ran perfect,

changed bosche maf and it ran awfull again,

did some tests,

compression test - perfect,
emmisions test - perfect (for purpose of seeing if cat was nakerd)

everything on cylinder 4 had been checked, so last thing was injector.

changed injector- idled abit ruff but missfire was gone and drove fine.

fast forward to last week, ran petrol down to 0 coz i was in middle of nowere and the station was shut, filled it up eventually, next morning massive missfire was back,

took it in yesterday and swopped the fuel filter, he ran it for an hour, all perfect, turned it off, started it again few hours later and it was missfiring again,

the missfire is only in 3rd - 5th and bad upto about 3k, or when you quickly put foot to floor, nothing happens for 1-2 seconds then it just bogs down missfiring upto 3k.



ive put abit of injector cleaner through it, but with everythign ive replaced what the hell could be left thats wrong with it? the guys seem to think it could be a ecu fault as one min its fine n the next its crap again,

fuel pump?