My TDI 110 started dropping into limp home mode at 3K revs a few years ago, I was mainly doing short runs in it at the time.
After doing a few months research of the possible cleaning options I managed to fix the
problem at very little cost. Just some extra diesel and almost a speeding ticket.
I put the engine under heavy load above 3K revs a number of times and that seemed to do the trick. First I just tried running at high revs, in third on the motorway at 4K revs for 5 miles. This didn’t do much other than give me a headache.
I then tried increasing the load on the engine above 3k revs. This involved driving a few miles up a local dual carriageway warming the car up and checking for speed cameras then coming back the other way flat out, holding the loud peddle down for as long as you dare. Did this a few times over a few weeks and that stopped the over boost.
My job has changed and I do a motorway commute most days with a couple of steep hills. Once every week or two I floor it up the one of the hills and make sure the engine is pulling over 3K revs. Haven’t had the over boost come back, plus it can be fun.
I guess it depends how far gone your turbo is, but I would recommend trying to ‘self clean’ it first.
If that doesn’t work a £5 can of over cleaner maybe worth a go, there are few videos on
Youtube showing this.
Personally I would try the water in the air inlet trick first, again videos on
youtube about this. Partly because I’m getting too old to be crawling under cars and I also don’t fancy a snapped exhaust stud on a car that’s over ten years old.
If all those failed only then would I consider paying to have the turbo reconditioned.