Checks
| Action
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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.
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Preliminary Checks
| Refer to Important Preliminary Checks in
Symptoms - Engine Controls
.
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Sensor Checks
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| • | Test for proper operation and performance of the oxygen sensor. |
| | Inspect the oxygen sensor for silicon contamination. Caused by fuel or the use
of improper 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 PCM to reduce the amount of fuel to the engine. |
| • | Test the ECT sensor for proper 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 proper MAP sensor operation. A MAP sensor that does not respond
quickly and accurately to manifold pressure changes may cause this symptom. |
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Fuel System Checks
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| • | 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 fuel -- gasoline -- in the fuel pressure regulator
vacuum hose, if equipped. This indicates a faulty gasoline fuel pressure regulator. |
| • | Inspect for proper operation of the cng fuel injectors. Refer to: |
| • | Test for proper EVAP Purge system operation. |
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Additional Checks
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| • | Inspect for manifold or air induction system leaks. |
| • | Test the PCV system for proper operation and valve type. |
| • | Test for proper engine cylinder compression. |
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