I have a 2003 SL500 and 2 Mercedes dealerships cannot figure out the problem. The "Check Engine" light comes on and the car starts running poorly, no power, engine missing, bad exhaust smell. The car had approx. 18,000 miles (February 2008) when the problem started; at least since the car is in my possession; I bought it pre-owned from a dealership with 100,000 miles guarantee that expired Nov.8, 2008. So, I thought I was safe. The first Mercedes Dealership, Phil Smart, Seattle, had the car for 14 days, did extensive testing and road tests, did replace some minor items under warranty, but never confirmed what the actual problem was. I drove the car for approx. 5,000 miles and the same problem resurfaced while I was visiting in Canada. Now, I brought the car to Wilson Mercedez, Bellingham, because they are closer and found out that the warranty just expired a couple of weeks ago. The car again drove rough and the service writer agreed that there is a problem when I brought it in. The next day they problem was gone and although they drove the car approx. 250 miles they could not re-create the problem and cannot figure out how to fix it. Does anybody have any idea?