Sometimes a shake or shudder will emanate from the engine compartment, because the engine isn't getting the proper amount of air, fuel or spark that it needs to run smoothly.
Symptoms that might indicate such an engine-related case of the shakes include the following:
- Shudder or jerking occurs during acceleration
- Staccato shaking, as if over a highway "rumble strip," within a specific speed range
- Car starts and drives fine for a while, but later begins to shake
These symptoms could be signaling that it's time for a new set of spark plugs. If the plugs are fine, it could be that the spark plug wires need to be checked (are they connected in the proper order?) or replaced.
Also consider that a dirty air filter or clogged fuel filter can starve the engine of needed oxygen or fuel, respectively. These filters are inexpensive and easy to swap out, so take a look at your owner's manual and be sure to replace filters at the manufacturer's recommended intervals.