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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| • | Inspect for fuel in the pressure regulator vacuum hose. |
| • | Ensure each injector harness is connected to the correct injector/cylinder. |
| • | Inspect for any items which may cause an engine to run rich (long
term fuel trim is significantly in the negative range). Refer to Diagnostic
Aids for DTC P0172. |
| • | Inspect for any items which may cause an engine to run lean (long
term fuel trim is significantly in the positive range). Refer to Diagnostic
Aids for DTC P0171. |
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Sensor/System
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| • | Test for conditions which cause an incorrect idle speed. |
| - | Restricted air intake system. |
| • | Inspect the air intake ducts for being collapsed, damaged areas,
looseness, improper installation, or leaking especially between the MAF
sensor and the throttle body. |
| • | Monitor the 24X Crankshaft Position and Camshaft Position Sensors
on 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 circuits for intermittents. Inspect the IC circuit,
Bypass circuit, 3X Reference High Circuit, and the 3X Reference Low circuit
for intermittents. If these circuits become open, or shorted may not set
a DTC immediately, but are capable of causing driveability complaints. Refer
to
Testing for Intermittent Conditions and Poor Connections
in Wiring Systems. |
| • | Inspect the Transaxle Range 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 proper ignition voltage output using the following
steps: |
| 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: |
| - | Coils--Cracks, carbon tracking/arcing, or a resistance value
outside the specified range. |
Coil Resistance
5000-8000ohms (5K-8Kohms) | - | Spark Plug wires--signs of arcing, cross firing, cracks,
carbon tracking, plug boot damage, pinched, improper routing, or a resistance
value outside the specified range. |
Spark Plug Wire Resistance
600ohms per foot (1 968ohms per meter).
| | Important: : Spraying the secondary ignition wires with a light mist of water may
help locate an intermittent problem. Ignition voltage will arc to ground when
a secondary component is faulty.
|
| - | Defective ignition module. |
| - | Ignition system wiring--Loose ignition module feed or ground
connection, or damaged system wiring. |
| • | Remove spark plugs and inspect for the following conditions: |
| - | Burned or damaged electrodes |
| - | Improper heat range or reach |
| • | If 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. |
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Engine Mechanical
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| • | Inspect 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: |
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Additional
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| • | Inspect exhaust system for possible restrictions: |
| - | Inspect exhaust system for damaged or collapsed pipes. |
| - | Inspect mufflers for heat distress or possible internal failure. |
| • | Inspect for faulty motor mounts. Refer to Engine Mechanical. |
| • | 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 problem exists, inspect the routing of secondary
ignition wires, high voltage components (Near Ignition Control
circuits). |
| • | Inspect for faulty motor mounts. |
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