For 1990-2009 cars

Checks | Action
--- | ---
DEFINITION: The engine power output varies under a steady throttle or cruise. The vehicle seems to speed up and slow down with no change in the accelerator pedal position.
Preliminary Checks |

• | Refer to Powertrain On Board Diagnostic (OBD) System Check .

• | Refer to Symptoms .

• | Educate the driver about normal A/C compressor operation.

• | Use a scan tool in order to verfy that the reading of VSS matches the reading of the vehicle speedometer.

Sensor Check |

• | Check the performance of the MAP sensor. Refer to DTC P0106 Manifold Absolute Pressure (MAP) System Performance Diagnostic Aids.

• | Check the performance of the heated oxygen sensor (HO2S) sensor 1 and the HO2S 2. Refer to Diagnostic Aids in DTC P0131 through DTC P0141.

Fuel System Checks |

• | Determine whether a rich or lean fueling condition can cause the concern. Drive the vehicle at the speed of the concern. Monitor the Fuel Trim parameters on a scan tool in order to identify the fuel system status.

- | Lean -- The Long Term Fuel Trim value will be greater than 20%. Refer to DTC P0171 Fuel Trim System Lean Diagnostic Aids.

- | Rich -- The Long Term Fuel Trim value will be greater than -20%. Refer to DTC P0172 Fuel Trim System Rich Diagnostic Aids.

• | Check the fuel pressure when the condition occurs. Refer to Fuel System Diagnosis .

• | Check the fuel injector for a conical spray pattern and even flow.

• | Check that the fuel injector electrical resistance is 0.5-1.5 ohms at 20°C (68°F).

• | Check for contaminated fuel or inferior quality fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

Ignition System Checks |

• | Check for the proper secondary voltage output with a J 26792 spark tester or an equivalent.

• | Check the spark plugs for any of the following conditions:

- | Wet (fuel fouled) plugs.

- | A terminal screw that is bent or loose (rotate and pull).

- | A ceramic insulator that has cracks, carbon tracking or deposits (red or black dust)

- | A tip insulator that has cracks, carbon tracking, deposits (oil, carbon, glazing, fuel additive), or is loose (rattles).

- | A center electrode that is loose (wiggles side to side)

- | An incorrect spark plug gap that is too wide or too narrow.

- | Platinum pads that are missing.

Additional Checks |

• | Check the PCM grounds for being clean, tight, and in the proper location. Refer to

#### PCM Power and Ground

.

• | Check the generator output voltage.

• | Check the vacuum lines and hoses for leaks or restrictions. Refer to the Vehicle Emission Control Information label for the correct routing of vacuum lines.

• | Check for an intermittent EGR problem. Refer to Exhaust Gas Recirculation (EGR) System Diagnosis .