what is wrong with my ford fiesta finnesse 2002?

my ford feista finesse when stationary is sitting at 1 and a half thousand revs, it has never done this before, i took it to a garage they said my idol valve may be blocked up, they cleaned it out and reset it, they did say it will take 20 to 30 starts for it to kick in, firstly does anyone know if this correct and if it is not what might it be?
some one has mentioned how it may be the throttle but they also said it would be expensive and just to put up with it, please help me!