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.

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

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Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

1. Perform a bulletin search.
2. If a bulletin that addresses the symptom is found, correct the condition as instructed in the bulletin.

Was a bulletin found that addresses the symptom?

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Go to Step 13

Go to Step 3

Was visual/physical check performed?

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Go to Step 4

Go to Important Preliminary Checks

1. Check the PCM grounds for being clean, tight and proper routing. Use the PCM wiring diagrams in Section 8A .
2. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 26

Go to Step 5

Observe the Long Term Fuel Trim on the scan tool.

Is Long Term Fuel Trim below the specified value (Rich condition)?

80

Go to Step 6

Go to Step 7

1. Check the items that can cause the engine to run rich. Refer to DTC P0172 Fuel Trim System Rich for diagnosis.
2. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 26

Go to Step 9

Is the Long Term Fuel Trim above the specified value (Lean condition)?

160

Go to Step 8

Go to Step 9

1. Check the items that can cause the engine to run lean. Refer to DTC P0171 Fuel Trim System Lean .
2. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 26

Go to Step 9

1. Check the IAC operation. Perform procedure in DTC P0506 Idle Speed Low diagnostic table.
2. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 26

Go to Step 10

1. Check the MAP sensor for proper operation. Refer to Manifold Absolute Pressure Sensor Output Diagnosis for further diagnosis.
2. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 26

Go to Step 11

Check the injector connections. If any of the injectors are connected to an incorrect cylinder, correct as necessary.

Was a problem found?

Go to Step 26

Go to Step 12

1. Perform the Fuel Injector Solenoid Coil Test or Fuel Injector Balance Test .
2. If a problem is found, repair as necessary.

Was a problem found?

Go to Step 26

Go to Step 13

1. Check for fuel in pressure regulator vacuum hose.
2. If fuel is present, replace the fuel pressure regulator assembly. Refer to Fuel Pressure Regulator Replacement .
3. If a problem is found, repair as necessary.

Was a problem found?

Go to Step 26

Go to Step 14

1. Check for proper ignition voltage output with the spark plug jumper wires J 36012 and spark tester J 26792.
2. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 26

Go to Step 15

Important: If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs in order to prevent further damage.

1. Remove the spark plugs, check for wet plugs, cracks, wear, improper gap, burned electrodes, or heavy deposits.

1. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 26

Go to Step 16

1. Check for loose ignition control module ground.
2. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 26

Go to Step 17

1. Check the ignition coils for cracks or carbon tracking.
2. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 26

Go to Step 18

Using a scan tool, monitor the TP angle with the engine idling.

Is the TP angle at the specified value and steady?

0%

Go to Step 19

Go to DTC P0123 Throttle Position (TP) Sensor Circuit High Voltage for further diagnosis

1. Check the Crankcase oil/air separator for proper operation. Refer to Crankcase Ventilation System Diagnosis .
2. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 26

Go to Step 20

1. Check for proper generator voltage output.
2. The voltage should be between the specified values.

Is the voltage between the specified values?

11-16V

Go to Step 21

Go to Section 6D

1. Check for proper A/C operation. A/C clutch should disengage at Wide Open Throttle.
2. If a problem is found, refer to Air Conditioning (A/C) Compressor Clutch Control Diagnosis for further diagnosis.

Was a problem found?

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Go to Air Conditioning (A/C) Compressor Clutch Control Diagnosis

Go to Step 22

1. Check the following engine mechanical items. Refer to Engine Mechanical for diagnosis procedures:

•	Check compression.

•	Sticking or leaking valves.

•	Worn camshaft lobe(s).

•	Valve timing.

•	Broken valve springs.

2. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 26

Go to Step 23

1. Check for malfunctioning motor mounts. Refer toEngine Mechanical for inspection of mounts.
2. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 26

Go to Step 24

1. Check the intake valves for valve deposits.
2. If deposits are found, remove as necessary.

Were deposits found on the intake valves?

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Go to Step 26

Go to Step 25

1. Review all diagnostic procedures within this table.
2. If all procedures have been completed and no malfunctions have been found, review/inspect the following items:

•	Visual/physical inspection.

•	Scan tool data.

•	All electrical connections within a suspected circuit and/or system.

3. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 26

Check for Service Bulletins

Operate vehicle within the conditions under which the original symptom was noted.

Does the system now operate properly?

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System OK

Go to Step 2