1999 Ford Festiva 1999 Ford Festiva over revs

Hey there,

I have a Ford Festiva, 1999 model. 160K's
It's been driving fine for the last 6 months. Suddenly, when driving last week it now over rev's when slowing down.
When changing down into 3rd and 2nd it rev's at 2,000 rpm, then when idle it flicks between 1,500 and 2,000 and then when the car stops, its rev's from 2,000 - 2,500 rpms! When you start from cold or warm, it revs at 2,000 rpms. Nothing seems wrong under the hood and the gas cable isnb't too loose.
I was thinking either the gas cable or the TPS(?) Sensor system?
Any help would be greatly appreciated.
Thanks.