Idle Adjustment Precautions

Idle speed is controlled by PCM and Idle Air Control (IAC) valve. If control system is operating properly, engine idle RPM is fixed and cannot be changed by standard adjustments. A scan tester must be used on these systems because control strategy and idle speed specification are controlled by PCM.

Before adjusting idle speed, complete a thorough basic inspection and self-tests (KOEO, KOER and continuous memory) to confirm correct operation of sub-systems contributing to idle speed control. See TESTS W/CODES article.

Ensure throttle bore and both sides of throttle plate(s) are clean, throttle plate does not stick in bore, and/or linkage is not limiting throttle plate operation. Throttle lever must rest on throttle stop screw. When IAC valve is disconnected, engine may stall. This is acceptable only if throttle plate and linkage are not stuck.

Throttle bodies use sludge resistant throttle plate designs on some models . These throttle plates must not be cleaned because of protective coating on lip of throttle plate(s). For location of sludge resistant throttle plate identification label, see illustration. See Fig 1 .

Ensure all accessories are turned off before checking and adjusting idle speed. Ensure cooling system is filled to correct level. Ensure vacuum leaks do not exist and unmetered air does not enter throttle chamber on mass airflow design systems. If vehicle is equipped with electric cooling fan, check and adjust idle speed when fan is off.

Fig 1: Locating Sludge Resistant Throttle Plate Labels

Courtesy of FORD MOTOR CO.

Idle speed is not adjustable. If engine idle concerns are present, check for contaminated fuel, vacuum leaks and incorrect ignition timing. Ensure throttle bore, EGR system and PCV system are clean. If these are okay, see TESTS W/CODES article for additional procedures.