I've recently purchased a 1995 M3, working it into a track car. It had several issues when I first purchased the car, so I took it to a trusted BMW mechanic to "clean" it up. Replaced the failed oxygen sensor, and the Mass Air Sensor, both of which were giving codes and causing the engine to run rich. New plugs, aircleaner, new fluids front to back and the car came out running great, except. . . .

After the car warms up, it begins to have a subtle irregular miss at idle. The tach doesn't change rpm, it just stumbles every 2-3 seconds. Otherwise it runs great. An interesting fact is, while the engine is warming up, NO miss. Another thing I've noticed, once in a while when I accelerate hard I hear what I think is spark knock. But I cannot force it to happen by crowding the engine in a high gear. This is very rare, so I don't know if it has any bearing on the idle problem.

During the first inspection, we found the crankcase re-circulation hose broken, which was leaking air, but this has been fixed. All other hoses and the intake plenum look good. So far no new codes, so any ideas of where to look?

One other fact, the compression check is showing all cylinders at 180+ lbs