knocking and bad idle, there's a chance the dumbass but 87 or something octane in it which isn't resistant enough for bimmer compression, smoke--was it cold? was it just started? what kind of maintainence? ask him how often and where he get his oil changed and what weight, maintainence and how it was treated is 100% of the life of the car, I've seen 50k mi beamers break down, mine has 250k and drives better than a brand new acura i used to have. The owner makes all the diff.