The MAF sensor on my 1999 528iT went bad recently, and so I ordered one of the "cheap" ones off eBay. I should have done my homework...Those "cheap" units from China are real junk. From the start my little 6 Cly. "chugged" a bit before coming up to idle. I did reset the OBD BTW with my Peake scanner after the initial install.
After a couple of weeks of giving the new unit a try, I kicked down the transmission to try and get in front of a 18 wheeler via the on ramp on I-75. "Bang" went the rear end, and the "Tranny" light kicked on.
After completing the "25-30 sec." re-set, and resetting the OBD with my Peake scanner, all was well; as long as I did not shift down to accelerate.
I did try something too. I disconnected the MAF sensor cable, and the "Tranny" light came on...After the reset, I installed a better grade/re-manufactured MAF, and the problems seem to have gone away.
I have followed several threads on this and other BMW blogs regarding MAF issues, and wished to chime in with my experience. Bottom line, the MAF sensor sends signals to the Engine AND Transmission computers...If the MAF is bad, even a little, it will affect the two.