For 1990-2009 cars

Checks | Action
--- | ---
DEFINITION: The engine-power output varies under a steady throttle or under a steady cruise. The vehicle seems to speed up and to slow down without any change in the accelerator pedal position.
Preliminary Checks |

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

• | Refer to Symptoms .

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

• | Use a scan tool in order to verify that the reading of the vehicle speed sensor (VSS) matches the reading of the vehicle speedometer. Vehicles with electronic transmissions are not included because some variation between the VSS readings and the speedometer readings are considered normal.

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.

| Check the performance of the HO2S 1 and of the HO2S 2. Refer to Diagnostic Aids in DTC P0131 through DTC P0141.

• | Check the reference signal from the CKP sensor with a scan tool. Observe the engine speed parameter while operating the engine at the speed of the concern. The scan tool should indicate steady RPM readings and linear RPM readings while running. If sudden increases or decreases in engine speed are displayed, the engine reference signal is not stable enough for the engine to run correctly. Check for a short to ground in the ignition reference low circuit of the CKP sensor. A short to ground in the ignition reference low circuit of the CKP sensor will cause a faulty engine reference signal to be sent to the PCM.However, this will not set a CKP sensor DTC.

Fuel System Checks |

• | Determine whether a rich fueling condition or a 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 will approach 20 percent. Refer to DTC P0171 Fuel Trim System Lean Diagnostic Aids.

- | Rich - The Long Term Fuel Trim will approach -20 percent. Refer to DTC P0172 Fuel Trim System Rich Diagnostic Aids.

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

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

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

Ignition System Checks |

• | Check for adequate secondary ignition voltage with a J 26792 spark tester or with an equivalent.

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

- | Wet plugs

- | A bent or loose terminal screw

- | A ceramic insulator that has cracks, carbon tracking, or deposits

- | A tip insulator that has cracks, has carbon tracking, has deposits, or is loose

- | A center electrode that is loose

- | An incorrect spark plug gap that is too large or too small.

Additional Checks |

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

#### Cell 21: Power and Ground

.

• | Check the generator output voltage.

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

• | Check the Service Bulletins for any updates.