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 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 will cause the control module
(Alternative Fuel ECM, gasoline VCM/PCM or ECM) 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. |
|
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 fuel or gasoline in the fuel pressure regulator vacuum
hose, if equipped. This indicates a faulty gasoline fuel pressure regulator. |
| • | Test for proper EVAP Purge system operation. |
| • | Inspect for proper installation of the bonnet and fuel mixer. |
| • | Inspect for air leaks at the fuel mixer. |
|
Additional
Checks
|
| • | Inspect for manifold or air induction system leaks. |
| • | Test the PCV system for proper operation and valve type. |
| • | Test for proper engine cylinder compression. |
|
