Have a similar issue with my son's 2000 (W) reg 1.25 zetec Fiesta.
Basically we've replaced the Throttle Position Sensor twice now (first time with a pattern part then with a genuine Ford item). Initially the problems were cured by fitting the pattern part and resetting the ECU by disconnecting the battery for 30 mins. However, the problem then returned - car idles when stationery at 1200 rpm, then "hunts" between 1900 and 2500 rpm if you blip the throttle. Put the car in gear and just move slightly and the revs drop back to idle again. When moving it's as though it has "cruise control" and wants to drive itself. We've now fitted a new genuine Ford TPS, and rectified a problem with a collapsed vacuum pipe which was causing the revs to stick at 3000rpm but still have the problem. Immediately after reconnecting the battery the car will idle at 1000rpm, but once you touch the throttle it's up to 1200 and then hunting again between 1900 and 2500rpm. I've checked the wiring to the sensor and the voltages - 5 volts in from the ECU, one pin to ground and the output back to the ECU on the centre pin at closed throttle is 0.2 volts (I'd read somewhere that over 0.4 volts can cause problems).

Please, has anyone got any other ideas ? My son is driving me mad moaning about having to keep spending money on it and I just don't know where to look next.

Thanks for any help or advice anyone can offer.