Inspections
| Action
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DEFINITION: The engine runs unevenly at idle. If severe, the engine or the vehicle may shake. Engine idle may vary in speed. Either condition may be severe enough to stall the engine.
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Preliminary
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• | Verify that the ECM and ECM bracket fasteners are at the correct torque. |
• | Inspect the intake air duct and air cleaner outlet resonator for the following conditions: |
- | Improperly installed hoses |
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Fuel System
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• | Verify that each injector harness is connected to the correct injector/cylinder according to the firing order. |
• | Test the items that cause an engine to run rich. For a rich condition, refer to
DTC P2178
or
DTC P2188
. |
• | Test the items that can cause an engine to run lean. For a lean condition, refer to
DTC P2177
or
DTC P2187
. |
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Sensor/System
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Ignition System
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• | Inspect for the correct installation of the ignition coil seals. Incorrect installation may allow water to enter the spark plug area. Inspect for moisture and corrosion. |
• | Remove the spark plugs and inspect for the following conditions: |
- | Refer to the following procedures: |
• | If the spark plugs are gas, coolant or oil fouled, determine the cause before replacing the spark plugs. Refer to the following procedures: |
- | For diagnosis of coolant contaminated spark plugs, refer to
Loss of Coolant
. |
• | Inspect the spark plug boots and terminals for burning or micro-arcing, corrosion, and damage to the insulation. |
• | Inspect the crankshaft position (CKP) sensor for the correct resistance. The sensor resistance may be out of range after a hot soak. Measure that the resistance remains within 700-1,200 ohms at all temperatures. |
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Engine Mechanical
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• | Inspect for the following engine mechanical conditions: |
- | Excessive oil in combustion chamber or leaking valve seals |
- | Incorrect cylinder compression |
- | Sticking or leaking valves |
- | Excessive carbon buildup in the combustion chambers--Clean the chambers with top engine cleaner. Follow the instructions on the can. |
- | For more information, refer to the following procedures: |
• | Inspect the following components for incorrect basic engine parts: |
- | Pistons, connecting rods, or bearings. |
- | Refer to the following procedures: |
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Additional
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• | Inspect the evaporative emissions (EVAP) canister purge solenoid for the following: |
- | Charcoal contamination due to a defective EVAP canister |
• | Inspect the following exhaust system components: |
- | The exhaust system components for damage |
- | The mufflers for heat distress or possible internal failure |
- | The three-way catalytic converters for restrictions |
• | Electromagnetic interference (EMI) on the CKP sensor signal circuits can cause an engine misfire condition. You can usually detect EMI with a scan tool by monitoring the engine speed parameter. A sudden increase in the engine speed parameter, with
little change in actual engine speed indicates that EMI is present. Inspect for high voltage components near the ignition control circuits if a condition exists. Also, inspect the engine ground shield of the CKP sensor circuits. |
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