Checks
| 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 Checks
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| • | Refer to the Powertrain OBD System Check. |
| • | Refer to Important Preliminary Checks. |
| • | Refer to Visual/Physical Checks |
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Fuel System
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| • | Check the fuel Pressure. Refer to Fuel System Pressure Test. |
| • | Check the injectors. Refer to Fuel Injector Coil/Fuel Injector
Balance test. |
| • | Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel
Testing. |
| • | Check for fuel in the pressure regulator vacuum hose. |
| • | Ensure each injector harness is connected to the correct injector/cylinder.
Refer to Engine Control Wiring Diagram. |
| • | Check items which can cause an engine to run rich (long term fuel
trim is significantly in the negative range). Refer to Diagnostic Aids for
DTC P0172. |
| • | Check items that can 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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| • | Check for conditions which cause an incorrect idle speed. |
| - | Throttle body tampering, excessive desposits, or damage. Refer
to Fuel Metering System Components. |
| - | Restricted air intake system. Refer to Air Induction System. |
| • | Check Crankcase ventilation valve for proper operation. Refer
to Crankcase Ventilation System. |
| • | Check the TP Sensor and related wiring. Refer to DTC P0123 Diagnosis. |
| • | Check the EGR system for proper operation. Refer to EGR System. |
| • | Check the Transaxle Range Switch input with the vehicle in drive
and the gear selector in drive or overdrive. Refer to Transaxle Range Switch
Valid Combinations. |
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Ignition System
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| • | Check for proper ignition voltage output using the following steps: |
| - | Clip the spark tester J 26792 to engine ground. |
| - | Connect one end of a spark plug wire to the spark tester; leave
the other end of the spark plug wire to the coil being tested. |
| - | Connect one end of another spark plug wire to the other coil tower;
connect the other end of the spark plug wire to ground. |
| - | Crank the engine while observing the spark tester; a crisp blue
spark should be observed. |
| - | Repeat the above steps for each coil. |
| • | If adequate spark is not present at the coil(s), check for the
following conditions: |
| - | Coil(s) - Cracks, carbon tracking/arcing, or a resistance value
outside the specified range. |
Coil Resistance
5000 - 8000 ohms (5K - 8K ohms) | - | 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
7000 ohms (7K ohms)
| | Important: Spraying the secondary ignition wires with a light mist of water may
help locate an intermittent problem. Ignition components will arc to ground
when a secondary component is faulty.
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| - | Ignition System Wiring - Loose ignition module feed or ground
connection, or damaged system wiring. |
| • | Remove spark plugs and check for the following: |
| - | 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. |
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Engine Mechanical
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| • | 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: |
| • | Refer to Engine Mechanical
for diagnosis
procedures. |
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Additional Checks
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| • | Check exhaust system for possible restrictions. Check for the
following: |
| - | Inspect exhaust system for damaged or collapsed pipes. |
| - | Inspect mufflers for heat distress or possible internal failure. |
| - | For possible plugged Three-Way catalytic converter. Refer
to Restricted Exhaust System Check and Exhaust System. |
| • | Check 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, check
routing of secondary ignition wires, high voltage components (Near Ignition
Control circuits). |
| • | Check for faulty motor mounts. Refer to Engine
Mechanical
for inspection of mounts. |
| • | Check for intake and exhaust manifold passages for casting flash.
Refer to Engine Mechanical.
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