Definition: Steady pulsation or jerking that follows engine speed, usually more pronounced as engine load increases, not normally felt above 1500 RPM or 48 km/h (30 mph). The exhaust has a steady spitting sound at idle, low speed or on hard acceleration for fuel starvation that can cause engine to cut out.

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

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Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Perform the careful visual/physical checks as described at the start of Symptoms section.

Was the visual/physical check performed?

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Go to Step 3

Go to Important Preliminary Checks

Is DTC P0300, P0301, P0302, P0303, or P0304 set?

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Go to applicable DTC table

Go to Step 4

1. Check the spark plugs for the following items:

•	Insulator cracks.

•	Improper gap.

•	Burned electrodes.

•	Heavy deposits.

2. If any of the above conditions were found, replace the spark plugs.

Did any of the plugs require replacement?

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Go to Step 13

Go to Step 5

1. Disconnect all injector harness connectors and install an injector test light J 34730-2 between the harness terminal connector of each injector.
2. Crank the engine and note the light on each connector. If test light fails to blink at any one of the connectors, it is a malfunctioning injector drive circuit harness, connector or terminal may be the fault.

Did the test light blink on all injector harness connectors?

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Go to Step 6

Go to applicable misfire DTC table

1. Check the fuel pressure. Perform procedure in Fuel System Diagnosis .
2. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 13

Go to Step 7

1. Check for contaminated fuel.
2. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 13

Go to Step 8

1. Perform Fuel Injector Solenoid Coil Test or Fuel Injector Balance Test .
2. Replace any injector found malfunctioning.

Were any injector(s) replaced?

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Go to Step 13

Go to Step 9

1. Check the engine mechanical for the following conditions. Refer to Engine Mechanical for diagnosis procedures.

•	Low compression.

•	Sticking or leaking valves.

•	Worn camshaft lobe(s).

•	Incorrect valve timing.

2. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 13

Go to Step 10

1. Check the Intake and exhaust manifold(s) for casting flash. Refer to Engine Mechanical section .
2. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 13

Go to Step 11

1. Check for Electromagnetic Interference (EMI). A missing condition can be caused by EMI on the reference circuit. EMI can usually be detected by monitoring engine RPM with a scan tool. A sudden increase in RPM with little change in actual engine RPM change, indicates EMI is present.
2. If EMI is present, locate and repair the source.

Was a problem found?

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Go to Step 13

Go to Step 12

1. Review all diagnostic procedures within this table.
2. If all procedures have been completed and no malfunctions have been found, review/inspect the following items:

•	Visual/physical inspection.

•	Scan tool data.

•	All electrical connections within a suspected circuit and/or system.

3. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 13

Check for Service Bulletins

Operate vehicle within the conditions under which the original symptom was noted.

Does the system now operate properly?

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System OK

Go to Step 2