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
Symptoms
, Important Preliminary Checks Before Starting.
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• | Check the PCM grounds for being clean, tight and in their proper
locations. Refer to PCM wiring diagrams
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Fuel System
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• | Check that each injector harness is connected to the correct injector/cylinder
according to the firing order (firing order: 1-8-4-3-6-5-7-2).
Relocate injector harnesses as necessary. |
• | Check for injectors that are shorted internally. Compare the injector
resistance. Injector resistance should be within one ohm of each other. Refer
to
Fuel Injector Solenoid Coil Test
. |
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Sensor/System
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• | Check the crankcase ventilation valve for proper operation. Place
a finger over inlet hole of the valve end several times. The valve should
snap back. If not, replace the valve. |
• | Check for silicon contamination from fuel or improperly used sealant.
The HO2 Sensor will have a white powdery coating. The HO2 Sensor will result
in a high but false signal voltage (rich exhaust indication). The PCM will
reduce the amount of fuel delivered to the engine causing a severe driveability
concern. For more information, refer to Information
Systems
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• | Use a scan tool in order to monitor KS system for excessive spark
retard activity. |
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Ignition System
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• | Remove spark plugs and check for the following: |
• | An improper spark plug gap will cause a driveability problem.
Refer to Engine Electrical/Spark Plug.
Do the
spark plug gapping using a wire gauge gap tool (J 41319). Refer to
Spark Plug Replacement. Determine the cause of the fouling before replacing
the spark plugs if spark plugs are gas or oil fouled. Refer to
Fuel System Diagnosis
or diagnosis of the rich condition
or Engine/Engine Mechanical
for diagnosis of the
oil fouling condition. |
• | Visually/Physically inspect Secondary ignition for the following: |
- | Ignition wires for cross firing |
- | Ignition wires arcing to ground |
- | Ignition wires for proper routing |
• | Wet down the secondary ignition system with water from a spray
bottle. Wetting down the secondary ignition system may help locate damaged
or deteriorated components. Look/listen for arcing or misfiring as you
apply water. |
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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 |
- | Low cylinder compression |
• | For incorrect basic engine parts. Inspect the following: |
Refer to Engine/Engine Mechanical
for
diagnosis procedures.
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Additional Checks
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• | Check the exhaust system for possible restrictions. Check for
the following: |
- | Inspect the exhaust system for damaged or collapsed pipes. |
- | Inspect the exhaust manifold for a collapsed inner wall. |
- | Inspect the mufflers for heat distress or possible internal failure. |
- | Inspect for possible plugged catalytic converters by comparing
exhaust system back pressure on each side of engine. Check the back pressure
by removing Heated Oxygen Sensor (HO2S) near exhaust manifolds. Refer to
Restricted Exhaust System Check and Exhaust System. |
• | Electromagnetic Interference (EMI) on the reference circuit can
cause an engine miss condition A scan tool can usually detect EMI by monitoring
the engine RPM. A sudden increase in RPM with little change in actual engine
RPM change, this indicates that EMI is present. If a problem exists, check
routing of secondary ignition wires or high voltage components near ignition
control circuits. |
• | Check the PNP switch circuit. Refer to Park/Neutral
Position (PNP) Switch System Diagnosis
. |
• | Check for faulty motor mounts. Refer to Engine/Engine
Mechanical
for inspection of the mounts. |
• | Check the intake manifold and the exhaust manifold passages for
casting flash. Refer to Engine/Engine Mechanical.
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• | Check for vacuum leaks. Vacuum leaks can cause a higher than normal
idle. |
• | Check for the EGR being ON while idling which will cause roughness,
stalling, and hard to start. Refer to EGR System Diagnosis
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• | Check the battery cables and ground straps. They should be clean
and secure. |
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