Problems with over-revving Ford KA ?

Hi I had to call out the RAC regarding my car which was revving up and down when stationary. He cleaned the idle valve and suggested that it was the airflow sensor. I took it to my local garage and they replaced the said sensor, cleaned the idle valve again only to find that the engine is now running too fast (over 2000 revs when stationary!) I now have to have the car towed to a Ford Dealer tomorrow. My garage have drawn a blank! If anyone has any ideas? It's an R-reg 1997 model. Thanks.