You have not said what engine is in your car or what year it is, but i would think you need to replace your "idle air control valve". This is approx £115.00 for 2.0 petrol models and pre facelift 1.8 litre models. It fits on the side of the throttle body and is a long cylinder shaped object with an electrical contact one end. If you have a late model model 1.8, i.e. 1999 onwards, you may need to change the complete throttle body assembly. Check with your local dealer before doing anything.
Jajabusta, October 2005