Mondeo 55plate diesel air leak and smoke problem?

Hi there I have a 55plate Mondeo 115bhp diesel and I have same sort of problem, when accelerating there is a big sound of air escaping and black smoke, and the car revs up and down by it's self when it is kept at the same speed like in cruise control (hunting I think someone said), could this be the same problem the boost pipe many thanks Steve p.