Turbo whistle and loss of power on Ford Transit - sticking variable vanes

Loss of power when overtaking, limp mode after pressing the accelerator hard and a louder-than-normal boost whistle are common signs of sticking variable-geometry turbo vanes on 2.2 and 2.4 TDCi engines. Soot jams the control ring, so the turbo either overboosts or produces too little boost, and the ECU cuts engine power. Before deciding to rebuild or replace the turbocharger, rule out less expensive faults with identical symptoms: leaks in the vacuum system that controls the vanes and a split or disconnected intercooler hose. The underlying cause also matters. Sticking vanes often result from driving only at low engine speeds and neglecting the EGR system, so the problem will return unless its source is corrected.