1999 Hyundai Elantra mileage: 110,000. This car idles fairly well in neutral or park but very rough in reverse and drive. I just replaced the engine with a used engine and it is doing the same things the old engine was doing. I replaced the plugs, wires, rotor button, cap, fuel injectors, set timing, etc. This engine also misfires in idle. I NEED HELP!
Check the motor mounts; a broken mount will allow the engine to shake excessively. Your car is equipped with a computer controlled engine management system. An independent auto service center can scan your computer for fault or error codes. The information should pinpoint the mal functioning components.