The (variable) vanes in the turbine get coked up with carbon from the exhaust, which causes the actuator to sieze or not move to its full extent, this in turn damages the electronic actuator, As far as i remember Ford wants to sell you a compete turbo unit w actuator, you can pick the actuators up on the bay, i heard a rumor that there is one part that fails (the motor?) and it is realatively cheap to replace

An EGR blanking plate fixes all faulty EGR valves, EML may come on but engine will otherwise run fine, costs about a fiver (solid, stainless steel)