When I bought my Z3 in the beginning of March 2012, it developed a rough idle. I was determined I could track it down and began throwing parts at it.
List of Parts:
In order to track down what causes rough idle you must understand the engine you are working with and what can cause the engine to misbehave. BMWs are extremely technical when it comes to programming and using sensor in conjunction with the motor. Everything must work together and everything must work correctly.