Checks
| Action
|
DEFINITION: Engine
runs unevenly at idle. If severe, the engine or vehicle may shake. Engine
idle speed may vary in RPM. Either condition may be severe enough to
stall the engine.
|
Preliminary Checks
|
| • | Search for service bulletins. |
|
Fuel
System
|
| • | Check the fuel composition sensor for accuracy. Perform the Fuel
Composition Test and compare the results. |
| • | Check the fuel filter for being plugged or restricted. |
| • | Check items which can cause an engine to run rich-- Long
Term FT significantly in the negative range. Refer to Diagnostic Aids for
DTC P0172 Fuel Trim System Rich
. |
| • | Check items that can cause an engine to run lean-- Long Term
FT significantly in the positive range. Refer to Diagnostic Aids for
DTC P0171 Fuel Trim System Lean
. |
| • | Check for proper operation of the evaporative emission (EVAP)
control system. |
|
Sensor/System
|
| • | If the stalling condition occurs when the A/C is turned ON or
when the transmission is put into gear, make sure the PCM recognizes the change
in state for the component and the IAC counts change accordingly. |
| • | Check for proper IAC operation with the scan tool. |
| • | Check the oxygen sensor (O2S 1). The O2S 1 should
respond quickly to different throttle positions. If not, check the O2S 1
for silicon or other contaminants from fuel or the use of improper
RTV sealant. The sensors may have a white powdery coating. Silicon
contamination causes a high but false O2S 1 signal voltage--rich
exhaust indication. The PCM will reduce the amount of fuel delivered
to the engine, causing a severe driveability condition. |
| • | Check for proper operation of the TP sensor. |
| • | Check for proper operation of the ECT sensor. |
|
Ignition
System
|
| • | Check for proper ignition voltage output with the J 26792
spark tester. |
| • | Check the spark plugs for the following conditions: |
| - | Cracks on the spark plugs |
| - | Improper spark plug gap |
| - | Burned electrodes or heavy deposits |
| • | If the spark plugs are fuel or oil fouled, the cause of the fouling
must be determined before replacing the spark plugs. |
| • | Check the ignition control module (ICM) for proper ground connection. |
| • | Check the ignition coils for cracks or carbon tracking. |
| • | Check the spark plug wires for the proper resistance and condition. |
|
Engine
Mechanical
|
| • | Check engine mechanical for the following: |
| - | Sticking or leaking valves |
| - | Excessive oil in combustion chamber and leaking valve seals |
| • | Inspect for the following incorrect basic engine parts: |
| • | Refer to appropriate diagnostic procedures in Engine Mechanical. |
|
Additional
Checks
| Check
the following components of the exhaust system for possible restrictions:
| • | Inspect exhaust system for damaged or collapsed pipes. |
| • | Inspect mufflers for heat distress or possible internal failure. |
| • | An engine miss condition can be caused by electromagnetic interference
(EMI) on the reference circuit. EMI can usually be detected by monitoring
engine RPM with a scan tool. A sudden increase in RPM with little
change in actual engine RPM change, indicates EMI is present. If a
condition exists, check routing of secondary ignition wires, high voltage
components--near ignition control circuits. |
| • | Check for malfunctioning engine mounts. |
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