Fiesta always idles at 1500rpm

My fiesta cosistently idles at 1500 rpm all the time regardless of engine temperature and I think this is causing increased petrol consumption too.

Its a 1.1 LX 1995, and has single point injection I think. Could the temperature sensor be playing up thuis fooling the engine into thinking its cold all the time and holding the revs up? I'm not sure how plausible this is as even when cold it should only idle at around 1200rpm?

Alternatively what else could it be - idle control valve?

Any ideas welcomed, cheers