I've got a 2007 BMW 328i with 219k miles. My service engine soon light came on with a diagnosis of a misfire in cylinders 2 & 4. I swapped the coils in cylinders 1 & 2 to see if the code would move, but no change. The motor runs smooth with no noticeable power loss and the SES light has now gone off on its own. A scan of the computer still shows the misfire recorded. Is the next step to swap a couple of spark plugs to see if the code moves? The spark plugs only have about 20k on them and are genuine BMW plugs and the coils are original to the car. If a plug swap shows no change, what next?