Originally Posted by Raptor102
I tried to find an answer to this but haven't seen anything yet so sorry if this is a duplicate. I have a check engine light and it pops code P0303 on my 2000 E320. It runs very rough at startup as it's idling and I have almost no accelleration. As I have 76K on the car I figured I'd change all the plugs at the same time while I was at it. I did change all of the plugs and definitely reseated all of the boots well. However I still have the exact same issues as far as the symtoms above. Am I looking at possible bad wires or the coil? Any ideas on how to verify if one or the other is bad? Thanks
Since the coils are interchangeable the easiest thing to do is swap #3 with one of the others (plug wires and all). If the problem moves then it's either the coil or the wires, the wires are suspect enough you could probably just replace them first. They're stunningly expensive (about $10 to $25 each depending on if you buy a complete set and where you buy them) so you might want to isolate it further, but that means pulling them out of the coils, which could damage good wires. Personally if you swap it and the misfire code moves from where it was to the new cylinder I would probably buy two wires and a coil and call it a day; that way you're covered.
If after swapping coils the misfire stays at #3 you have other issues, but try the swap first and see where that leads you.
Take care and enjoy the ride,