find out the last time it had a oil change. zetec need the rite oil in them if the worng oil has bin put in can cause it too run rough. and if the oil get too dirty aswell it runs rough and can cut out you need 5w-30w oil and a filter. if that dnt work try a new idle control valve if that dnt work you need to start looking at other things like blocked cat or engine manangement problems ecu etc. hope that has helped