P0300 is for Engine Cylinder Misfire

check EGR valve
check injector connectors
possible bad injector, check injector with a long screwdriver to hear the injectors click when the engine is running to make sure the injector is working.
Possible bad ignition coil. check this too.
check spark plugs, you may have a bad spark plug.
check fuel filter and fuel pressure. if pressure is bad, possible bad fuel pump.