you might have a air leak on the induction side get some brake cleaner get the car running and spray the brake cleaner all around the
induction area like the throttle body, inlet manifold that sort of thing be careful not to spray it on the exhaust manifold,if the revs pick up when you are spraying it that means you have an air leak in that area so try to pin point it down if nothing happens with the revs you don't have a air leak..........................thanks Rik