The Idle Air Control (IAC) valve on a 2001 Ford Ranger 4.0L engine is located on the throttle body. It's a small, usually black, electrically controlled valve mounted directly to the throttle body itself. You'll likely find it on the side of the throttle body, facing either the engine or the firewall, depending on the specific orientation of the components in your vehicle's engine bay.
To be sure, you should consult a repair manual specific to your 2001 Ford Ranger 4.0L. A picture in the manual will clearly show its location. You can also search online for "2001 Ford Ranger 4.0L IAC valve location" along with images. This should give you several visual references to help you pinpoint it.
