The Idle Air Control (IAC) valve on a 2001 Ford Escort ZX2 (assuming that's the model you have, as there were different body styles) is located on the throttle body. It's a small, usually cylindrical, electronic component mounted directly to the throttle body itself. You'll find the throttle body near the intake manifold, at the top of the engine. It's connected to the engine's intake by a rubber hose.
To be absolutely certain, you'll need to consult a repair manual specific to your 2001 Ford Escort's engine (there were different engine options). A diagram will show the IAC valve's exact position. You can find these manuals online or at auto parts stores.
