1999 Nissan Maxima

I am getting the error code P1320 for my 99 Nissan Maxima. The code states a ignition misfire. I read all the suggestions and followed most of them without success of getting the light to go out. I replaced on the ignition coils, spark plugs (NGK's). when replacing the plugs, I did notice that there was oil on one of the plugs. I changed the valve covers to eliminate that problem. Could oil on the ingnition coil cause the plug to misfire or create the error code. Additionally, what other suggestions are there to remedy this problem. thanks in advance.