Hi. we had the same problem with an older mondeo 2L. we found it was very tempermental and sometimes 'jumped'. (Kids called it the kangeroo car).we took it to the garage and it was a very small hole in the vaccum pipe. thus it was temperamental due to the level of moisture and heat under the bonnet. Worth checking the pipe for any noticable cracks or holes. if you cant find one, try replacing whole pipe. Hope this helps.
Julia, March 2011
