the dealership miss-diagnosed the car and didnt fix the problem? damn i would have lost it on them. usually i would have said MAF but if you got that covered. do me a favor. check the intake elbow. on the bottom should be i think two air tubes. make sure they are on nice and snug. (im really not sure if its two because i have a 6cly)
now if that seem clear. take off the intake elbow and check for blockage in one of the tubes.
thats a start, i cant think of anything else right now. all i can say is take it back to the dealership and complain.
good luck and welcome to BWM-forums.
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