I have a 2009 328xi sedan manufactured 07/09 and was experiencing idle flutter at a stop. After going through several forum threads from different sources I was hearing that this was related to a vacuum leak. However, when I stopped by a local mechanic to schedule a service for this he mentioned the possibility of one or more coils being defective. He had also pointed out that I had an air pump so the vacuum from the brakes was unlikely. I was unable to schedule the service due to my schedule but I did act on his assessment and ordered 6 new Bosch coils and 6 new spark plugs. It took me about an hour to replace all the coils and plugs (once I got the correct plugs). It turns out that the threaded portion of the initial plugs I ordered, Bosch ZGR 6 STE 2, were too skinny for the engine. What caused this was that my 2009 changed in mid-year. So I called the vendor BMA auto parts and they were very helpful in working with me to exchange these for the OEM NGK PLZFR6A plugs. And for the normal shipping they overnighted them to me from CA to MA. Needless to say the engine runs great and this DIY project cost me just $207.