it really bugs me when i hear stories like this , ive got an E53 x5 diesel, and the fuel injectors started to leak back and prevented the car from starting...cost about 400 pounds to fix, but still didnt run right, after reading through these forums i started a process of elimination, bought a new maf sensor- £99 from germany...car started running 75% better though at 3500 revs wouldnt change gear (downshift to accelerate) i then bought and fixed the cam sensor...now it accelerates beautifully 95% better, over the weekend im going to change the crank sensor, i believe that should make my car sweet...total savings from not using the stealership?...my sanity and at least 500 quid as all parts cost me less than 200 pounds.
just for every ones info, you can actually service fuel injectors, those of you in UK and near wokingham google alan Darby...at lynxdiesels.com might save you loads of dosh.
MAF sensors can be gotten from airmassmeters.com...the guys name is paul and quick delivery...50- 75% cheaper than BMW. hope this info is helpful