There are several different vehicle components that cause engines to shake, shudder or vibrate. CarsDirect.com lists worn or faulty spark plugs as the most common cause of engine vibration. Bad spark plugs cause an engine to misfire or not fire at all on some or all cylinders. This throws the engine out of balance, resulting in vibration.
Loose or disconnected vacuum hoses, an improperly adjusted or poorly working fuel intake system and loose timing belts are a few of the more easily remedied causes of engine vibration. Solving vacuum issues is often as simple as replacing or reconnecting hoses, and loose timing belts are fixed through a timing belt change where the belt, idlers and tensioner are replaced to ensure a tight fit. CarsDirect.com recommends cleaning the fuel intake, throttle body or the carburetor, as well as readjusting components to manufacturer specifications to eliminate vibration caused by the fuel intake system.
Damaged or broken motor mounts are arguably the most serious cause of engine vibration. CarsDirect.com suggests that a driver shift between drive and neutral while the vehicle is sitting still. If the vibration lessens while in neutral, the motor mounts may have sustained damage. Changing old motor mounts requires lifting the engine to access the mounts, a repair with high labor costs.