Inspection/Test
| Action
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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.
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Preliminary
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Fuel System
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| • | Test the fuel injectors. Refer to the following procedures: |
| • | Inspect for fuel in the pressure regulator vacuum hose. |
| • | Ensure each injector harness is connected to the correct injector
and cylinder. |
| • | Inspect for any items which may cause an engine to run rich.
Refer to the Diagnostic Aids for DTC P0172. |
| • | Inspect for any items which may cause an engine to run lean.
Refer to the Diagnostic Aids for DTC P0171. |
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Sensor/System
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| • | Test for the following conditions which cause an incorrect idle
speed: |
| - | A restricted air intake system |
| • | Inspect the air intake ducts for collapsed ducts, damaged areas,
looseness, improper installation, or leaking, especially between the MAF
sensor and the throttle body. |
| • | Monitor the 24X crankshaft position (CKP) sensor and the camshaft
position (CMP) sensor on the scan tool. If both are not responding, test the
sensor feed circuit. Both sensors use a separate feed circuit but are internally
connected to power. Test all 24X and CMP sensor circuits for intermittents.
Refer to
Testing for Intermittent Conditions and Poor Connections
in Wiring Systems. |
| • | Monitor the 3X parameter on the scan tool. If the 3X is not responding,
inspect the 7X CKP sensor and the circuits for intermittents. Inspect the
ignition control (IC) circuit, the bypass circuit, the 3X reference high
circuit, and the 3X reference low circuit for intermittents. If these circuits
become open or shorted, a DTC may not set immediately, but the circuits
are capable of causing driveability complaints. Refer to
Testing for Intermittent Conditions and Poor Connections
in Wiring Systems. |
| • | Inspect the Transaxle Internal Mode Switch input with the vehicle
in Drive and the gear selector in Drive or Overdrive. |
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Ignition System
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| • | Inspect for the proper ignition voltage output using the following
procedure: |
| 1. | Attach the J 26792
spark tester to engine ground. |
| 2. | Connect the spark plug end of the spark plug wire to the J 26792
spark tester. Leave the
other end of the spark plug wire connected to the coil being tested. |
| 3. | Connect the spark plug end of the companion spark plug wire to
ground. |
The companion spark plug wire is the wire attached to the corresponding
coil tower.
| 4. | Crank the engine while observing the J 26792
spark tester. A spark should be observed. |
| 5. | Repeat the above steps for each coil. |
| • | If spark is not present at the coils, inspect for the following
conditions: |
| - | Check the coils for cracks, carbon tracking or arcing, or a resistance
value outside the specified range. |
Coil Resistance
5,000-8,000 ohms | - | Check the spark plug wires for signs of arcing, cross-firing,
cracks, carbon tracking, plug boot damage, pinching, improper routing, or
a resistance value outside the specified range. |
Spark Plug Wire Resistance
1 968 ohms per meter (600 ohms per foot).
| | Important: : Spraying the secondary ignition wires with a light mist of water may
help locate an intermittent problem. The ignition voltage will arc to ground
when a secondary component is faulty.
|
| - | Test for a defective ignition module. |
| - | Inspect the ignition system wiring for a loose ignition module
feed or ground connection, or damaged system wiring. |
| • | Remove the spark plugs and inspect for the following conditions: |
| - | Burned or damaged electrodes |
| - | Improper heat range or reach |
| • | If the spark plugs are gas or oil fouled, the cause of the fouling
must be determined before replacing the spark plugs. Refer to
Spark Plug Visual Diagnosis
in Engine Electrical. |
|
Engine Mechanical
|
| • | Inspect or test for the following engine mechanical conditions: |
| - | An incorrect compression |
| - | Any sticking or leaking valves |
| - | Any worn camshaft lobes |
| - | An incorrect valve timing |
| - | Any broken valve springs |
| - | Any excessive oil in the combustion chambers and leaking valve
seals |
| • | Inspect the following components for incorrect basic engine parts: |
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Additional
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| • | Inspect the exhaust system for restrictions: |
| - | Inspect the exhaust system for damaged or collapsed pipes. |
| - | Inspect the mufflers for heat distress or internal failure. |
| - | Inspect for a plugged three-way catalytic converter. |
| • | Inspect for faulty motor mounts. |
| • | 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 the
RPM with little change in the actual engine RPM indicates
EMI is present. If a problem exists, inspect the routing of secondary
ignition wires and the high voltage components near the ignition
control circuits. |
| • | Inspect the intake manifold passages and the exhaust manifold
passages for casting flash. |
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