I've ordered some MAF cleaner so when it arrives I'll get on this and see whats what. If cleaning it doesnt do the trick I'll steal the one from the M3 and see if that sures it - at least that way I can rule out a faulty MAF
If its faulty you should notice no difference when you run it unplugged....not sure who makes what types but my experience on other vehicles is that the two main manufacturers are Hitachi (expensive but ultra-reliable) and Bosch (cheap but unreliable, partly because of their self-cleaning cycle which can eventually burn the wire out).