Rough, Unstable, or Incorrect Idle, Stalling
Checks
| Action
|
DEFINITION: The engine
runs unevenly at idle. If the condition is severe, the engine or the vehicle
may shake. The 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 filter for plugs or restrictions. |
| • | Check items which can cause an engine to run rich, where long-term
fuel trim is significantly in the negative range. Refer to
DTC P0172 Fuel Trim System Rich
. |
| • | Check items that can cause an engine to run lean, where long-term
fuel trim is significantly in the positive range. Refer to
DTC P0171 Fuel Trim System Lean
. |
| • | Check for proper operation of the evaporative emission (EVAP)
control system. |
| • | Check for fuel in the fuel pressure regulator vacuum hose. |
|
Sensor/System
|
| • | 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
room-temperature vulcanizing (RTV) sealant. The sensors may
have a white powdery coating, indicative of silicon contamination , which
causes a high but false O2S 1 signal voltage, indicating
a rich exhaust. The PCM will reduce the amount of fuel that
is delivered to the engine, causing a severe driveability problem.
Refer to
Serial Data Communications
. |
| • | Check for proper operation of: |
|
Ignition System
|
| • | Check for proper ignition voltage output with the 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, determine the cause
of the fouling 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-Leaking valve seals |
| • | For incorrect basic engine parts -- Inspect the following: |
| - | Other engine parts as appropriate |
|
Additional Checks
| Check the exhaust system for possible restrictions. Check
for the following:
| • | Inspect the exhaust system for damaged or collapsed pipes. |
| • | Inspect the 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
the engine RPM with a scan tool. A sudden increase in RPM with little
change in the actual engine RPM indicates that EMI is present.
If a problem exists check the routing of the secondary ignition wires,
or check the high voltage components near the ignition control circuits. |
|
