I keep getting error code for number 4 engine coil misfire. So i bought new coils and spark plugs so i started to replace all of them. When I got to the number 4 spark plug it had oil on it. The others didn't. How do I fix the oil issue? I'm sure that's why it misfires according the the check engine light OBD2 reader. Looking for some advise and hows to's?