Normal
Okie, the charging of ur battery at 13.9V is normal and won't cause any problems. The prob ur are having seems to point to a sensor problem. Try checking the connection for the Air Flow Sensor (AFS). It is connected just after the air filter and it takes the form of a black square plastic box with a wire harness connected to it. Unplug it, check the connector to see if its wet or dirty, then plug it back in again. Twitch it a little when u plug it back in...