Rough, Unstable, or Incorrect Idle, Stalling
Checks
| Action
|
DEFINITION: The engine runs unevenly during idle. If the condition is
severe, the engine or the vehicle may shake. The engine idle speed
may vary in revolution per minute (RPM). Either condition may be
severe enough to stall the engine.
|
Preliminary Checks
|
| • | Search for service bulletins. |
|
Fuel
System
|
| • | Inspect the fuel filter for plugs or for restrictions. |
| • | Inspect for conditions which can cause an engine to run rich,
where long-term fuel trim is significantly in the negative range. Refer to
DTC P0172
. |
| • | Inspect for conditions that can cause an engine to run lean, where
long-term fuel trim is significantly in the positive range. Refer to
DTC P0171
. |
| • | Ensure proper operation of the evaporative emission (EVAP) control
system. |
| • | Inspect for fuel in the fuel pressure regulator vacuum hose. |
|
Sensor/System
|
| • | Inspect the oxygen sensor (O2S 1). The O2S 1 should
respond quickly to different throttle positions. If not, inspect the O2S 1
for silicon or for other contaminants from the fuel, or from 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 powertrain control module (PCM) will reduce
the amount of fuel that is delivered to the engine, causing a
severe driveability problem. |
| • | Ensure proper operation of: |
| - | The manifold absolute pressure (MAP) sensor |
| - | The throttle position (TP) sensor |
| - | The engine coolant temperature (ECT) sensor |
|
Ignition
System
|
| • | Ensure proper ignition voltage output with the J 26792
Spark Tester or equivalent. |
| • | Inspect 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. |
| • | 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 the engine mechanical components for the following conditions:
| • | Sticking or leaking valves |
| • | Excessive oil in combustion chamber due to leaking valve seals |
| • | For incorrect basic engine parts--Inspect the following components: |
| - | Other engine parts as appropriate |
|
Additional
Checks
| Inspect
the exhaust system for possible restrictions. Inspect for the following conditions:
| • | Damaged or collapsed pipes in the exhaust system. |
| • | Heat distress or possible internal failure of the muffler. |
| • | A possible plugged three-way catalytic converter (TWC). Refer
to
Engine Mount Inspection
in Engine
Mechanical-2.2L. |
| • | An engine miss condition can be caused by electromagnetic interference
(EMI) on the reference circuit. EMI can usually be detected by monitoring
the engine revolutions per minute (RPM) with a scan tool. A sudden increase
in the RPM, with little change in the actual engine RPM indicates
that EMI is present. If a problem exists, inspect the routing
of the secondary ignition wires, or inspect the high voltage components
near the ignition control circuits. |
|
