Jerkin/Missing on petrol and backfiring on cng(like cracker), i tuned it up, change spark plugs, cleaned throttle, cleaned injectors. Mechanic said that coil should be replaced (its already taped) and due to this old one this causes otherwise no missing when you put pedal smoothly, but suddenly you put accelerator it vibrates something, please help should i replaced or not or having tuned cng via laptop?