I have a 2003 BMW 530d Auto (E60) that has done 124,000 miles. I recently experienced a sort of power lag, by this I mean when doing speeds of 75 - 85 mph and you press the accelerator (not kick-down but a progressive push) to overtake, the car increases speed but does not have that "torque feeling" that you'd expect. I also noticed that there was a consistant pushing, as if the car wanted to go but didn't. This happened three or four times, and then the car went as it should. A specialist changed the Mass Air Flow sensor and, for 10 minutes, the power was resumed. After 15 mins of motorway driving, every time I floored the accelerator, I was getting plumes of black soot-like fumes coming from the exhaust which were visible in my rear view mirror. Could you please advise as to what the problem could be?