Its on the intake manifold. back side about middle. Below the TB and when installed on the motor above the starter. Its a PITA to get to but I have found its best to go from the bottom. you have to do most of it by feel and don't have a whole lot of room to swing wrenches so is a little slow going to back out the I believe 10mm (two) bolts.
Their is a write up IIRC on the cleaning of this. think you basically just use Carb cleaner and some Que tips and let it dry then re-install. hardest part is putting the gasket back on since you cant really see what your doing.
2001 ZX3 2.0L Zetec-
Hatch Nation #42
Going through Rebuild See "The TICK Build Thread" for details (http://www.focusfanatics.com/forum/showthread.php?t=289168&referrerid=62897)