The idle air control (IAC) valve on a 1998 Ford Ranger is designed to raise or lower the idle by regulating the amount of air that enters the throttle body. As the valve opens, more air is allowed to enter the throttle body raising the engine speed. The IAC valve is controlled by the powertrain control module (PCM). The PCM constantly adjusts the position of the IAC valve in order to maintain a stable, smooth idle. When the IAC valve fails the engine may stall or idle erratically.
Start the engine and place the gear selector in the “P” position.
Locate the car’s diagnostic port below the steering column, just under the dashboard.
Power on the scan tool and plug it into the diagnostic port. Navigate to the bi-directional test menu and select the IAC valve.
Use the scan tool to open and close the IAC valve. If the engine speed does not raise and lower as the valve is open and closed, then it is faulty.
