For 1990-2009 cars

Checks | Action
--- | ---
DEFINITION: Engine power variation under steady throttle or cruise. Feels like the vehicle speeds up and slows down without a change in the accelerator pedal position.
Preliminary |

• | Refer to Important Preliminary Checks Before Starting in Symptoms - Engine Controls .

• | Search for bulletins.

• | Inspect the ECM grounds for being clean, tight, and in the proper locations. Refer to Engine Controls Schematics .

• | Be sure the driver understands the operation of the transmission torque converter clutch (TCC) and A/C compressor operation as explained in the owner's manual. Inform the customer how the TCC and the A/C clutch operates.

Sensor/System |

• | Test the heated oxygen sensors (HO2S). The HO2S should respond quickly to the different throttle positions. If they do not, inspect the HO2S for silicon or other contaminates from fuel or the use of improper RTV sealant. The sensors may have a white powdery coating. This type of contamination may result in a rich exhaust indication. The engine control module (ECM) will then reduce the amount of fuel delivered to the engine, causing a severe driveability condition.

• | Inspect the CKP sensor and wiring for an intermittent condition. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

• | Inspect the intake air ducts for proper installation and for leaks.

• | Inspect the mass air flow (MAF) sensor connections. Repair or replace the terminals. Refer to Connector Repairs in Wiring Systems.

Fuel System |

• | Inspect the fuel system. Refer to Fuel System Diagnosis .

• | Test for incorrect fuel pressure.

• | Test for a restricted fuel filter.

• | Test for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

• | Verify that each injector harness is connected to the correct injector/cylinder. Relocate injector harnesses as necessary.

• | Test the fuel injectors. Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) .

• | Test the items which can cause an engine to run rich (long term fuel trim near -13 percent). For a rich condition, refer to DTC P0172 or P0175 .

• | Test the items that can cause an engine to run lean (long term fuel trim near 23 percent). For a lean condition, refer to DTC P0171 or P0174 .

Ignition System |

• | Inspect for proper installation of the ignition coil seal. Improper installation may allow water to enter spark plug area. Inspect for evidence of water that may have evaporated.

• | Test for proper ignition voltage output with a J 26792 Spark Tester. Refer to Electronic Ignition (EI) System Diagnosis . If you suspect secondary ignition system leakage, perform the procedure in the Diagnostic Aids portion of the Ignition System Check.

• | Remove the spark plugs and inspect for the following conditions:

- | Correct heat range

- | Wet plugs

- | Cracks

- | Wear

- | Improper gap

- | Burned electrodes

- | Heavy deposits

• | An improper spark plug gap may cause a driveability condition. Gap the spark plugs using a wire gauge gap tool. Refer to Spark Plug Replacement .

• | Determine the cause of the fouling before replacing the spark plugs if the spark plugs are gas, coolant or oil fouled. Refer to Spark Plug Inspection . Once you determine the cause of the fouling, refer to one of the following procedures:

- | For diagnosis of a rich condition, refer to DTC P0172 or P0175 .

- | For diagnosis of coolant contaminated spark plugs, refer to Loss of Coolant in Engine Cooling.

- | For diagnosis of oil fouled spark plugs, refer to Oil Consumption Diagnosis in Engine Mechanical-3.0 (L81).

Additional Checks |

• | Visually/physically inspect vacuum hoses for splits, kinks, and proper connections and routing as shown on the vehicle emission control information label. Refer to Emission Hose Routing Diagram .

• | Inspect the exhaust system for the following conditions:

- | Damaged or collapsed pipes

- | Heat distress or for an internal failure of the muffler

- | Restricted exhaust--Refer to Restricted Exhaust in Engine Exhaust.

• | Test the transmission torque converter clutch (TCC) operation. A TCC applying too soon can cause the engine to spark knock. Refer to Torque Converter Diagnosis in Automatic Transmission-4L30-E.

• | Test the A/C clutch for proper operation. Refer to Symptoms - Engine Controls in HVAC Systems Automatic.