i used to work for skoda and had loads of pd lumps overboost, 9 times out of 10it was the turbo, we just replaced them, when it was that the problem occurred when on full load 5th/6th gear, car had plenty of power then just lost its power giving you no turbo, stop the car then restart it was ok till on full load again, you would get an overboost fault code
as for cleaning i did one at home, took turbo off then soak in mr muscle for a couple of days, then put back on it was spot on