Not exactly the same, but previously I had an Audi 2.0 TDi. It had the standard variable vane turbo problem, meaning it over boosted and went into limp mode. I took it to my local Audi specialist and they recommended the `Forte` range of cleaners. It wasnt cheap, £40 for the turbo cleaner one they done (2 bottles) but the garage said it was worth a go before they did anything like changing out the turbo, and they recommended it to many customers and had positive results back. They said I would have to buy it online as they didnt sell it. I did what it said on the bottles, and run it on BP Ultimate, as the garage said this was also worth doing at the same time. I didnt expect it to work, but it actually did. I went from it going into limp mode 2-3 times a week to never doing it again while I owned it.
I was always suspicious of these things, but for this one, the VVT Cleaner by Forte, it worked a treat. I might buy a bottle or two of their cleaners for my TD5, cant do any harm.