DEFINITION: A jerking that follows engine speed, usually more pronounced as the engine load increases which is not normally felt above 1500 RPM or 48 km/h (30 mph).

Preliminary Check

Refer to Symptoms .

Ignition System Checks

Check for a cylinder misfire:

1. Start the engine.
2. Allow the engine to stabilize.
3. Then disconnect the Idle Air Control (IAC) motor.

Notice: Do not perform this test for more than 2 minutes in order to prevent damaging the catalytic converter.

4. Perform the Cylinder Power Balance Test with a scan tool.
5. If there is a RPM drop on all cylinders (equal to within 50 RPM), refer to Rough, Unstable, or Incorrect Idle and Stalling .
6. Reconnect the IAC motor with the ignition OFF.
7. If there is no RPM drop on one or more of the cylinders, or excessive variation in drop, check for spark on the suspected cylinders with a J 26792 spark tester or equivalent.
8. If there is no spark, refer to Enhanced Ignition System Diagnosis .
9. If there is spark, remove the spark plugs in these cylinders and check for the following conditions:

•	Insulation cracks

•

Wear

•	Improper gap

•	Burned electrodes

•	Heavy deposits

-	Check the spark plug wire resistance (should not exceed 30,000 ohms).

-	Check the distributor rotor and the distributor cap.

-	If the previous check did not find the problem, visually check the following items:

•	The ignition system for moisture, dust, cracks, burns, etc.

•	With the engine running, spray the plug wires with a fine water mist to check for shorts.

•	Perform the Fuel Injector Balance Test. Refer to Fuel Injector Balance Test .

Engine Mechanical Checks

Fuel System Checks

Additional Check