I have an 08 535 with approximately 25,000. The car now has now developed a rough idle. I notice at a stop light the rpm's seem to drop and then come back up. I have already had three fuel pumps in the car and I am not getting any messages such as "Reduced Power...". If I am driving the car it seems to run normal. I have gone through a couple of tanks of gas so I don't think that is the problem. Any ideas?