Idle Speed: Notes
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 checking 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 the TESTS W/CODES - EEC-IV (3.2L SHO) article in the ENGINE PERFORMANCE section.
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 to set minimum air rate, engine may stall. This is acceptable only if throttle plate and linkage are not stuck.
Throttle bodies use sludge resistant throttle plate designs. 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 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 idle speed when fan is off.