I had my very over coddled Skoda Fabia TDI with a VNT turbo for ten years and drive it like my great, great granny. It does forty miles four times a week down a 60 mph max A road and nothing else. 2000 revs all the way, mostly behind big trucks and rarely more than 2500. So come sixty thousand miles, I get the over boost problem and limp mode overtaking a truck on a hill at sixty miles an hour. Found my way to this excellent thread and looked at what is involved. At seventy, I am less inclined to crawl under the car and burrow into the exhaust manifold than I used to be, so instead, I read the experiences of the contributors and thought about whether I could free the vanes up by the Italian Tune Up Method.
So, I drove it to the red line and held it just under, in second and third on the said A road for about twenty miles. I did this a couple of times and it gradually started to improve. I could still get it into limp mode, but it was happening under more sustained hammering. Then I hit on the idea of blasting it from a roundabout up a long hill in third and pumping the throttle on and off at about 70 up hill. Full throttle and off, full throttle and off. The reasoning here is I was trying to work that vane actuator mechanism and to make the vanes change back and forth to clear the carbon obstruction. The hill is a couple of miles long. After a bit of this treatment, I am pleased to say that I can't get it to go into limp mode anymore.
I am giving it the beans up that hill every trip these days and will keep doing it. You have to be cruel to be kind sometimes.