Rough idle and Check engine light???
I have a '96 328is with 147,000 miles on it. It has been realitivly trouble free until last week. Recently when I first would start the car when the engine was cold it would give a little bit of rough idle, but if I hit the throttle, it would rev with no problem, so only bottom end idle was affected. Shortly after that (unrelated I think), the water pump failed and I had it replaced (regrettably) at a BMW shop because it was a holiday and no one else was open. Check engine light came on that day too because the engine overheated. I only replaced the water pump, not the thermostat. Check engine light was off after we left the BMW shop in Wichita. After about 700 miles, my check engine light came back on and when I first start the car on a cold engine now, it gives a very rough idle and if I don't hit the throttle it will die until the engine warms a little. Seems to be getting worse though, and I'm not sure it is going to idle with a warm engine here after too long. Fine at any engine speed other than idle though, that is what is strange to me. Any ideas? I hate to start randomly replacing parts. Seems like potential problems are O2 sensors, Mass Airflow sensor, Idle control valve, who knows what else.
Thanks in advance.