For 1990-2009 cars

## Rough, Unstable, or Incorrect Idle and Stalling Petrol

Checks | Action
--- | ---
DEFINITION: The engine runs unevenly at idle. If severe enough, the engine or vehicle may shake. The engine idle speed may vary in RPM. Either condition may be severe enough to stall the engine.
Preliminary Checks | Refer to Important Preliminary Checks in Symptoms - Engine Controls .
Sensor Checks |

• | Test for correct operation and performance of the oxygen sensor.

| Inspect the oxygen sensor for silicon contamination. Caused by fuel or the use of incorrect engine sealants, the oxygen sensor will have a white, powdery coating. The sensor will output a high, but false signal voltage. This false rich condition may cause the LPG ECM to reduce the amount of fuel to the engine.

• | Test the ECT sensor for correct operation by performing the following:

1. | Allow the engine temperature to reach ambient air temperature by leaving the engine OFF for several hours - overnight for most accurate results.

2. | Turn the ignition ON while leaving the engine OFF.

3. | Using a scan tool compare the ECT and IAT sensors displayed temperature.

The sensors should be within 3°C (5°F) of each other.

4. | Replace the ECT sensor or repair the ECT sensor circuit if the ECT is not near the expected value.

• | Test for correct MAP sensor operation. A MAP sensor that does not respond quickly and accurately to manifold pressure changes may cause this symptom.

Fuel System Checks |

• | Determine if the condition is rich or lean by performing the following:

- | Operate the vehicle under the conditions of the concern.

- | Monitor the oxygen sensor output.

• | Test for leaking fuel injectors.

• | Inspect for correct operation of the LPG fuel injectors. Refer to:

| Fuel Injector Balance Test with Special Tool

• | Test for correct EVAP Purge system operation.

• | Test for correct alternative fuel system pressures. Refer to Fuel System Diagnosis .

Additional Checks |

• | Inspect for manifold or air induction system leaks.

• | Test the PCV system for correct operation and valve type.

• | Test for correct engine cylinder compression.