P0300 I had a water pump go out and the ses light came on with an obvious miss. Random missfire is a p0300. I changed the water pump and the opti and to my surprise the miss was still there. I looked into it and found that the antifreeze caused a problem with the # 7 spark plug wire. I changed the wire and the misss went away. This may help some of you. My wires were pretty old so I was not so surprised.