Could be a DSA valve. Needed mine replaced around 100k. I had similar symptoms which were a rough idle after the engine had fully warmed up. Engine speed would fluctuate between 600 and 800 RPM (M54 - 530i). Did not throw any messages in iDrive until I was taking the car in for repairs (what a coincidence huh).
Last edited by dwlink; 01-11-2013 at 02:49 PM.