Definition: The engine runs unevenly at idle. If the symptom is severe, the engine or the entire vehicle may shake. The engine idle speed may vary in RPM. Either condition may be severe enough to stall the engine.

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

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Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

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

Did you find a bulletin that addresses the symptom?

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Go to Step 13

Go to Step 3

Perform the careful visual/physical checks as described at the start of the Symptoms section.

Did you perform a visual/physical check?

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Go to Step 4

Go to Important Preliminary Checks

1. Check the PCM grounds for being clean, tight and the proper routing. Use the PCM wiring diagrams in Electrical Diagnosis .
2. If a problem is present, repair the problem as necessary.

Was a repair necessary?

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Go to Step 26

Go to Step 5

Observe the Long Term Fuel Trim on the scan tool.

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

70

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 present, repair the problem as necessary.

Was a repair necessary?

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Go to Step 26

Go to Step 9

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

165

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 present, repair the problem as necessary.

Was a repair necessary?

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Go to Step 26

Go to Step 9

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

Was a repair necessary?

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Go to Step 26

Go to Step 10

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

Was a correction necessary?

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 present, repair the problem as necessary.

Was a repair necessary?

Go to Step 26

Go to Step 13

1. Check for fuel in the 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 present, repair the problem as necessary.

Was a repair necessary?

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 present, repair the problem as necessary.

Was a repair necessary?

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Go to Step 26

Go to Step 15

Notice: If spark plugs are gas or oil fouled, determime the cause of the fouling before replacing the spark plugs in order to avoid damage to the new spark plugs.

1. Remove the spark plugs and check for the following conditions:

•

Wet plugs

•

Cracks

•

Wear

•	An improper gap

•	Burned electrodes

•	Heavy deposits

2. If a problem is present, repair the problem as necessary.

Was a repair necessary?

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Go to Step 26

Go to Step 16

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

Was a repair necessary?

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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 present, repair the problem as necessary.

Was a repair necessary?

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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 a proper operation. Refer to Crankcase Ventilation System Diagnosis .
2. If a problem is present, repair the problem as necessary.

Was a repair necessary?

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Go to Step 26

Go to Step 20

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

Is the voltage between the specified values?

11-16 V

Go to Step 21

Go to Powertrain Control Module Controlled Generator Diagnosis

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

Was a problem present?

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

Go to Step 22

1. Check for the following engine mechanical conditions and refer to Engine Mechanical for the diagnosis procedures:

•	The compression

•	Sticking or leaking valves

•	Worn camshaft lobe(s)

•	Incorrect valve timing

•	Broken valve springs

2. If a problem is present, repair the problem as necessary.

Was a repair necessary?

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Go to Step 26

Go to Step 23

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

Was a repair necessary?

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Go to Step 26

Go to Step 24

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

Were there any deposits on the intake valves?

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Go to Step 26

Go to Step 25

1. Review all of the diagnostic procedures within this table.
2. If all of the procedures have been completed and no malfunctions are present, visually/physically inspect the following items:

•	The scan tool data

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

3. If a problem is present, repair the problem as necessary.

Was a repair necessary?

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Go to Step 26

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

Does the system now operate properly?

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System OK

Go to Step 2