1986 535i e28...When I first crank the car in the mornings from sitting overnight, the car cranks, idles and runs fine. BUT as the engine heats up and I leave for work, I lose acceleration, and the car starts to sputter and spit really bad. When I coast down hill with my foot off the accelerator (but clutch still engaged) the car tends to backfire a bit, or sputter even worse. When I come to a stop and the car is idling, it sounds like a Harley or something as the car revs while it is at idle...not much, but enough to notice. Could this be an oxygen sensor giving me trouble?