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
|
| • | Inspect the fuel composition sensor for accuracy. Perform the
Fuel Composition Test and compare the results. |
| • | Inspect the fuel filter for being plugged or restricted. |
| • | Inspect items which can cause an engine to run rich-- Short
term FT significantly in the negative range. Refer to Diagnostic Aids for
DTC P0172
. |
| • | Inspect items that can cause an engine to run lean-- Short
term FT significantly in the positive range. Refer to Diagnostic Aids for
DTC P0171
. |
| • | Inspect 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 powertrain control module
(PCM) recognizes the change in state for the component and the idle air control
(IAC) counts change accordingly |
| • | Inspect for proper IAC operation using the scan tool. |
| • | Inspect 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 problem. |
| • | Inspect for proper operation of the manifold absolute pressure
(MAP) sensor. |
| • | Inspect for proper operation of the throttle position (TP) sensor. |
| • | Inspect for proper operation of the engine coolant temperature
(ECT) sensor. |
|
Ignition System
|
| • | Inspect for proper ignition voltage output with a J 26792
Spark Tester or equivalent. |
| • | Check the spark plugs for the following conditions: |
| - | Wet or fuel fouled spark plugs |
| - | 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. |
| • | Inspect the ignition control module (ICM) for proper ground connection. |
| • | Inspect the ignition coils for cracks or carbon tracking. |
| • | Inspect the spark plug wires for the proper resistance and condition. |
|
Engine Mechanical
|
| • | Inspect 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: |
|
Additional Checks
| Inspect 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 CKP reference circuit. EMI can usually be detected by monitoring
medium resolution counter with a scan tool. A reading other than zero indicates
EMI is present. If a problem exists, check routing of secondary ignition wires,
high voltage components--Near ignition control circuits. |
| • | Inspect for malfunctioning engine mounts. |
|
