My 99 Fored Expediton is acting out again. Just recently I had replaced my spark plug wires because they were arching and the hesitation went away. Now its back the hesitation/misfire. I geting codes P0300 and P0171. Sometimes when I stomp on the gas it clears and other times the check engine light flashes like its trying to clear. Could it be that my spark plugs need to be replaced?

 

P0300 is a random misfire. The CEL is flashing because it is under a misfire condition at that moment. The P0171 is a lean code bank 1. Check for vacuum leaks, especially around the PCV hose on both ends. Make sure all vacuum hoses are hooked up properly. Most likely, the lean condition is causing the misfire. If it continues to misfire, it will set a code to a particular cylinder P030x. The last number will be the cylinder.