DEFINITION: The engine runs unevenly at idle. If the condition is severe, the engine or 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 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 a bulletin that addresses the symptom is present, correct the condition as instructed in the bulletin.

Did you find a bulletin that addresses the symptom?

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Go to Step 20

Go to Step 3

Did you perform a visual/physical check?

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Go to Step 4

Go to Symptoms

1. Check the ECM grounds for being clean, tight and for proper routing.
2. If a problem is present, repair as necessary.

Did you find a problem?

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Go to Step 20

Go to Step 5

Observe the Long Term Fuel Trim on the scan tool.

Is the Long Term Fuel Trim significantly in the negative range (Rich condition)?

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Go to Step 6

Go to Step 7

1. Check the conditions that can cause the engine to run rich.
2. If a problem is present, repair as necessary.

Did you find a problem?

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Go to Step 20

Go to Step 9

Is the Long Term Fuel Trim significantly in the positive range (Lean condition)?

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Go to Step 8

Go to Step 9

1. Check the conditions that can cause the engine to run lean.
2. If a problem is present, repair as necessary.

Did you find a problem?

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Go to Step 20

Go to Step 9

1. Check for an incorrect idle speed. Before checking, make sure that the following conditions are met:

•	The engine is at the normal operating temperature.

•	All of the accessories are off.

•	The transmission is in P/N.

2. Monitor the long term fuel trim with a scan tool.

Is the long term fuel trim skewed excessively positive or negative?

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Go to Step 11

Go to Step 10

1. Visually/physically inspect for the following conditions:

•	A restricted air intake system--Check for the following items:

-	A possible collapsed air intake duct

-	A restricted air filter element

-	Any foreign objects that could be blocking the air intake system

•	Excessive deposits in the throttle bore and on the throttle plate.

•	A large vacuum leak--Check for a condition that causes a large vacuum leak, such as an incorrectly installed or malfunctioning crankcase ventilation valve or a disconnected brake booster hose.

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

Did you find a problem?

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Go to Step 20

Go to Step 10

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

Did you perform a repair?

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Go to Step 20

Go to Step 12

1. Check for any fuel in the pressure regulator vacuum hose.
2. If there is fuel present, replace the fuel pressure regulator assembly. Refer to Fuel Injector and Fuel Rail Replacement .
3. If a problem is present, repair as necessary.

Did you find a problem?

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Go to Step 20

Go to Step 13

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

Did you find a problem?

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Go to Step 20

Go to Step 14

With the engine idling, monitor the throttle position (TP) angle with a scan tool.

Is the TP angle at the specified value and steady?

0%

Go to Step 15

Go to DTC P1220 Throttle Position (TP) Sensor 2 Circuit

1. Ensure that the crankcase ventilation valve is operating properly.
2. If a problem is present, repair as necessary.

Did you find a problem?

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Go to Step 20

Go to Step 16

1. Check the transmission range switch circuits with a scan tool. Be sure that the scan tool indicates that the vehicle is in drive with the gear selector in drive or overdrive.
2. If a problem is present, diagnose and repair the transmission range switch as necessary. Refer to Transmission Fluid Check .

Did you find a problem?

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Go to Step 20

Go to Step 17

1. Check in Engine Mechanical for the following problems:

•	Low compression

•	Sticking valves

•	A hydraulic valve lifter problem

•	Leaking cylinder head gaskets

•	Worn or incorrect camshaft

•	Incorrect cam timing

•	A damaged timing belt

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

Did you find a problem?

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Go to Step 20

Go to Step 18

1. Check for a damaged engine mount. Refer to Engine Mechanical for the proper inspection procedure.
2. If a problem is present, repair as necessary.

Did you find a problem?

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Go to Step 20

Go to Step 19

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

•	Perform a visual/physical inspection.

•	The scan tool data

•	The Freeze Frame data

•	All of the electrical connections within the suspected circuit and/or system

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

Did you find a problem?

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Go to Step 20

Go to Step 3

Operate the vehicle under the same conditions, as closely as possible, as when the original symptom occurred.

Is the original symptom still present?

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Go to Step 3

Go to Step 21

Are there any other driveability symptoms still present?

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Go to Symptoms

System OK