With Scan Tool

Description
The engine idle speed is controlled by the powertrain control module (PCM) through the idle air control (IAC) valve. The IAC valve opens and closes the idle air (bypass) passage in the throttle body according to signals from the PCM. The PCM determines the correct engine idle speed by using information from various sensors and switches. The PCM increases IAC duty (increases the opening in the idle air passage) when engine speed drops below a specified value. The PCM maintains a smooth and stable idle by monitoring certain engine components in order to respond to changes in engine load. The engine idle speed is a factory set calibration and is not adjustable.

Diagnostic Aids
DO NOT attempt to adjust the IAC valve or the throttle valve opening. The engine IAC valve and idle speed are not adjustable. Operate the IAC valve with the scan tool by selecting the appropriate Output Control feature. Command the IAC valve to increase and decrease engine idle speed. Diagnose and replace the faulty component or locate and repair the cause of the idle concern. Check for any of the following conditions if the IAC valve fails to control engine speed when commanded by the scan tool:
^ Vacuum leaks.
^ Blockage of the idle air (bypass) passage.
^ Improper PCV system operation.
^ Excessive accessory engine loads.
^ A faulty IAC valve.
^ Faulty electrical connections in the IAC valve electrical circuit.

Check the A/C Idle-Up circuit if the engine idle speed is a concern when the air conditioning or windshield defroster are running. Refer to A/C Idle Circuit Diagnosis. Component Tests and General Diagnostics

Check the Electrical Load Idle-Up Signal circuit if the engine idle speed is a concern when the headlights, blower motor, or rear defogger are on.

Refer to Electrical Load Idle-Up Signal Diagnosis. Component Tests and General Diagnostics

Test Description
The numbers below refer to the step numbers in the Diagnostic Table.
1. The Powertrain OBD system check prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
2. This step checks the engine idle speed with the engine at normal operating temperatures and no load. DO NOT attempt to adjust the IAC valve or the throttle valve opening. The engine IAC valve and idle speed (throttle valve opening) are not adjustable. Locate and replace the faulty component or repair the cause of the idle concern.
3. This step checks that the opening in the idle air (bypass) passage of the IAC valve is within the expected percentage (value). A DTC P0505 may set if this parameter stays outside of the specified value.
4. This step checks for vacuum leaks or faulty connections in the fuel injection and [1][2]EVAP control systems.
5. This step checks the accelerator control cable for a binding or misadjusted condition.