This problem if not with my BMW but with my honda. It is a problem that could happen to any car so I thought I'd run it by you guys to see if anyone had experienced the same problem with one of their cars. When I start the car and drive it, everything operates well when the engine is cold. After it warms up, there is rough performance at lower rpms. While I can't rule out the rotor, cap, and wires, it just doesn't seem likely. My reasoning for this is that the car operates normally when cold. The rpm only breaks up at the lower end of the rpm range. At higher rpm's, I can really wind out the engine without it breaking up. Also, if I am very careful in EASING the gas petal during acceleration, there is no break-up at lower rpms. Could it be dirty injectors?