Has the fuel pump ever been replaced? If not that's probably the problem...
If so have you replaced the fuel filter? Any vacume leaks? Also if the the throtal position sensor is going bad it will do this, but the CEL would always be on with a P0122 code...
EDIT: Also make sure you MAS sensor is pluged in (on the airbox line thing)
2000 Ford Focus US Spec Zetec 5 speed "Blue Dragon"
2000 Renault Clio 1.4 DOHC 5speed "Snap Dragon"
Hatch Nation #32