Inspections
| 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 Inspections
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Fuel System
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• | Inspect that each fuel injector harness is connected to the correct injector/cylinder.
Relocate fuel injector harnesses as necessary. |
• | Inspect for the following that may cause the engine to run rich: |
Notice: Refer to Heated Oxygen and Oxygen Sensor Notice in the Preface section. - | Water intrusion in the HO2S connector |
- | Engine oil contaminated by fuel |
- | An EVAP canister purge condition |
- | An inaccurate manifold absolute pressure (MAP) sensor |
- | An inaccurate mass air flow (MAF) sensor |
- | Blockage on the inlet screen of the MAF sensor |
- | Vacuum hoses that are split, kinked, or improperly connected |
- | An air intake duct that is collapsed or restricted |
• | Inspect for the following conditions that may cause the engine to run
lean: |
Notice: Refer to Heated Oxygen and Oxygen Sensor Notice in the Preface section. - | Water intrusion in the HO2S connector |
- | An exhaust leak between the HO2S and the engine--Refer to
Exhaust Leakage
in Engine Exhaust. |
- | An inaccurate MAP sensor |
- | An inaccurate MAF sensor |
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Sensor/System
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• | Inspect the crankcase ventilation valve for proper operation. Place
a finger over the inlet hole of the valve end several times. The valve should
snap back. If not, replace the valve. Refer to
Positive Crankcase Ventilation Valve Replacement
in Engine Mechanical. |
• | Use a scan tool in order to monitor the knock sensor (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: |
Refer to
Spark Plug Inspection
.
• | Determine the cause of the fouling before replacing the spark plugs. |
• | Visually and physically inspect secondary ignition for the following: |
- | Ignition wires arcing to ground |
- | Ignition wires for proper routing |
• | Soak the secondary ignition system with water from a spray bottle. Soaking
the secondary ignition system may help locate damaged or deteriorated components.
Look and listen for arcing or misfiring as you apply water. |
| Monitor
the Misfire Current Counters while driving the vehicle in the conditions that the
misfire occurred. If a misfiring cylinder can be located, use the DTC P0300
table for diagnosis. Refer to
DTC P0300
. |
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Engine Mechanical
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• | Inspect engine mechanical for the following: |
- | Sticking or leaking valves |
• | For incorrect basic engine parts. Inspect the following: |
Refer to
Symptoms - Engine Mechanical
in Engine Mechanical for diagnosis procedures.
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Additional Inspections
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• | Inspect the exhaust system for possible restrictions. Inspect for the
following: |
- | Inspect the exhaust system for damaged or collapsed pipes. |
- | Inspect the mufflers for heat distress or possible internal failure. |
- | Inspect for possible plugged catalytic converters. Refer to
Restricted Exhaust
in Engine Exhaust. |
• | 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
indicates that EMI is present. If a problem exists, inspect routing of secondary
ignition wires or high voltage components near the ignition control circuits. |
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