For 1990-2009 cars

Checks | Action
--- | ---
DEFINITION: The engine has a power variation under a steady throttle or cruise. The vehicle feels as if it speeds up and slows down with no change in the accelerator pedal.
Preliminary Checks |

• | Refer to Diagnostic System Check - Engine Controls .

• | Refer to Symptoms - Engine Controls .

• | Be sure the driver understands the A/C compressor operation.

• | Use a scan tool to make sure the reading of vehicle speed sensor (VSS) matches vehicle speedometer. This excludes vehicles with electronic transmissions where some variation between VSS and the speedometer is normal.

Sensor Check |

• | Check the performance of the mass air flow (MAF) sensor. Refer to Diagnostic Aids in DTC P0101 .

• | Inspect the operation of the heated oxygen sensor (HO2S) 1. Refer to:

- | DTC P0131

- | DTC P0132

- | DTC P0133

- | DTC P0134

• | Inspect for a shifted or fixed engine coolant temperature (ECT) sensor. Test the ECT sensor using the scan tool. Compare the engine coolant temperature with the ambient air temperature on a cold engine. If the engine coolant temperature is more than 5°C (9°F) more or less than the ambient air temperature, check for a high resistance in the coolant sensor circuit or the sensor itself. Refer to Temperature Versus Resistance .

Fuel System Checks |

• | Check if a Rich or Lean system can cause the condition. Drive the vehicle at the speed of the complaint. Monitoring the Fuel Trim may help identify the problem.

- | Lean--The Long Term Fuel Trim will be more than 20 percent. Refer to DTC P0171 .

- | Rich--The Long Term Fuel Trim will be less than -20 percent. Refer to DTC P0172 .

• | Check the fuel injectors. Perform the Fuel Injector Coil Test Procedure and the Fuel Injector Balance Test Procedure. Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) and Fuel Injector Balance Test with Special Tool .

• | Check the fuel pressure while the condition exists. Refer to Fuel System Diagnosis .

Ignition System Checks |

• | Check for the proper secondary voltage output with a J 26792 spark tester, or an equivalent. Refer to Electronic Ignition (EI) System Diagnosis .

• | Inspect the spark plugs for correct operation and performance. Refer to Spark Plug Inspection .

Additional Checks |

• | Check the powertrain control module (PCM) grounds and engine grounds for clean and tight connections in the correct locations. Refer to

#### Power and Ground

Engine Controls Components
MIL and DLC
Handling ESD Sensitive Parts Notice
H/L, HTR, IG and LAMP Fuses
HAZ, D/L, TAIL, STOP and DOME Fuses
BATT, ABS, FI and ACC Fuses
BATT, ABS, FI and ACC Fuses
Handling ESD Sensitive Parts Notice
G100, G101 and G102
.

• | Check the generator output voltage.

• | Check the vacuum lines and hoses for kinks or leaks. Review the Vehicle Emission Control Information label.

• | Check for an intermittent exhaust gas recirculation (EGR) problem.