i had my tentoioner gasket replaced and valve covers done. but when i picked up my car from the shop, check engine was on. they scanned it and pulled up code P0305. THEY REPLACED INJECTOR,SAME PROBLEM. CHANGED SPARK PLUGS, SAME PROBLEM. KNOW THEY SAY IT MAY BE THE COIL PACK. THE CAR IS MISFIRING AND I DID NOT HAVE THIS PROBLEM UNTIL THEY PUT THE CAR BACK TOGETHER. PLEASE HELP