Does it sound like it's coming from behind the dash in the centre?

The controller for the inlet manifold runner control is bolted to the bulkhead and the plastic linkage can break on the manifold where the cable is connected from the controller to the manifold. Pretty cheap fix, is your engine fault light on too?

This is the controller, check that it's not just the plastic linkage broken before replacing the whole thing tho!
http://www.fordpartsuk.com/shop/focu...l_imrc_813.htm