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DEFINITION: Steady pulsation or jerking that follows engine speed, usually more pronounced as engine load increases. This condition is not normally felt above 1,500 RPM or 48 km/h (30 mph). The exhaust has a steady spitting sound at idle or low speed.

Preliminary
    • Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls .
    • Search for bulletins.
    • Verify that the powertrain control module (PCM) grounds are clean, tight, and in the proper locations. Refer to Power and Grounding Component Views and Engine Controls Schematics .
    • Remove the air filter element and inspect for dirt and for restrictions. Refer to Air Cleaner Element Replacement . Replace as necessary.

Sensor/System
    • Test the fuel injectors. Refer to Fuel Injector Diagnosis .
    • Test for incorrect fuel pressure. Refer to Fuel System Diagnosis .
    • Inspect for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Inspect for the following conditions that may cause the engine to run rich:

Notice: Refer to Heated Oxygen and Oxygen Sensor Notice in the Preface section.

       - Any water intrusion in the heated oxygen sensor (HO2S) connector
       - The engine oil contaminated by fuel
       - Incorrect fuel pressure--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
       - Any leaking fuel injectors--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
       - Any vacuum hoses that are split, kinked, or improperly connected
       - An air intake duct that is collapsed or restricted--Refer to Air Cleaner Inlet Duct Replacement .
       - An air filter that is dirty or restricted--Refer to Air Cleaner Element Replacement .
    • Inspect for the following conditions that may cause the engine to run lean:

Notice: Refer to Heated Oxygen and Oxygen Sensor Notice in the Preface section.

       - Any water intrusion in the HO2S connector
       - An exhaust leak between the HO2S and the engine--Refer to Exhaust Leakage .
       - Any vacuum leaks
       - Incorrect fuel pressure--Refer to Fuel System Diagnosis .
       - Any restricted fuel injectors--Refer to Fuel Injector Diagnosis .
       - Fuel contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
       - Any vacuum hoses that are split, kinked, or improperly connected
    • Inspect for throttle body tampering, excessive deposits, or damage.
    • Inspect the crankcase ventilation system for proper operation. Refer to Crankcase Ventilation System Inspection/Diagnosis .

Ignition System
    • In order to properly inspect the spark plugs or to correct a condition, refer to the following procedures:
       -  Spark Plug Inspection
       -  Spark Plug Replacement
    • Remove spark plugs and inspect for the following conditions:
       - Correct heat range
       - Wet plugs
       - Cracks
       - Wear
       - Improper gap
       - Burned electrodes
       - Heavy deposits
       - Verify that the spark plugs are of the correct type.
    • Inspect for proper ignition system output. Refer to Electronic Ignition (EI) System Diagnosis .
    • An improper spark plug gap will cause a driveability condition. Gap the spark plugs using a wire gage gap tool.
    • Determine the cause of the fouling before replacing the spark plugs.
    • Inspect for damaged or misaligned spark plug boots.
    • Inspect the electronic ignition (EI) module for proper ground connection.
    • Monitor the Misfire Current Counters while driving the vehicle in the conditions that the symptom occurred. If a misfiring cylinder can be located, use the DTC P0300 table for diagnosis. Refer to DTC P0300 .

Engine Mechanical
    • Inspect engine mechanical for the following conditions:
       - Compression
       - Sticking or leaking valves
       - Worn camshaft lobes
       - Valve timing
       - Worn rocker arms
       - Broken valve springs
       - Excessive oil in combustion chamber or leaking valve seals.
       - For more information, refer to one or more of the following procedures.
    • For incorrect basic engine parts, inspect the following components:
       - The camshaft--Refer to Camshaft Cleaning and Inspection .
       - The cylinder heads--Refer to Cylinder Head Cleaning and Inspection .
       - The pistons, etc.--Refer to Piston, Connecting Rod, and Bearing Cleaning and Inspection .
    • Refer to Symptoms - Engine Mechanical for diagnosis procedures.
    • Inspect for excessive crankshaft endplay that will cause the crankshaft position (CKP) sensor reluctor wheel to move out of alignment with the CKP sensor. Refer to Camshaft Cleaning and Inspection . This could result in any of the following conditions:
       - A no start
       - A start and stall
       - Erratic performance

Additional Inspections
    • Inspect the exhaust system for the following possible restrictions:
       - The exhaust system for damaged or collapsed pipes
       - The mufflers for heat distress or possible internal failure
       - The catalytic converters for being plugged--Refer to Restricted Exhaust .
    • Electromagnetic interference (EMI) can cause an engine misfire condition. A sudden increase in indicated RPM with little change in actual engine RPM change indicates EMI is present. Inspect for high voltage components near ignition control circuits if a condition exists.
    • Inspect the intake manifold and the exhaust manifold passages for casting flash.