TIMING BELT SHOULDN,T CAUSE A RANDOM MISSFIRE , HOWEVER A STICKY INJ , BAD PLUGS AND OR OIL IN THE PLUG TUBES WOULD DEFINATELY THROW A CEL LIGHT , MAKE CERTAN YOU HAVE THE CORRECT PLUGS AND THAT THERE IS NO OIL IN THE BOTTOM OF THE PLUG TUBES AND IF YOU CAN GET THE BG INJ CLEANER AND GIVE IT A SHOT IF IT HAS NEVER BEEN DONE TO YOUR ENG AND THEN POUR A CAN OF THE CLEANER IN THE FUEL TANK ALONG WITH A CAN OF DRY GAS OR A BOTTTLE OF RUBBING ALCOHOL YOU MAY BE GETTING WATER IN YOUR FUEL WHICH WILL CAUSE IT TO THROW RANDOM MISSFIRES ALLSO