Idling fault? any ideas.....

My car seems to have developed an idling problem.......After it has been running, it sometimes idles at around 1200 rpm! A quick tap on the accelerator pedal usually brings it back down to around 750 ish rpm (although it happens again after!)
Any ideas????

sounds like it could be your throttle position sensor (http://vbxmaxima.8m.com/tps.html)

Maybe the throttle cable is getting stuck somehow and when you tap the accelerator like you said its letting it loose again. When you see it idling at over 1000 rpm's try first checking this cable under the hood and instead of tapping the accelerator try pulling the cable a little towards the outside of the car.

But do this when it has warmed up to eliminate the possibility of cold idling. If its still cold it could still idle at high rpm's.