I am trying to fix a problem with a '01 Trooper Limited 4WD. The vehicle has 75,000 miles and started to sound rather rough. My wife had the vehicle checked at a shop and was told the EGR valve was bad. I replaced the part as well as a new set of plugs, reset the OBD codes and the car runs a lot better. I am still getting a P0300 code (multilple engine misfire) and the check engine light blinks only when the car is moving. It does not blink when the car is not moving even if the same RPM level is reached. What is causing this misfire?