I don't know the answers to those questions. I would assume a like for like replacement on the turbo but as you have said it could be one of many. I checked the vacuum pipe today which goes to the black cylindrical box bolted to the inner wing and the pipe had a good suction. Don't get me wrong, when I hit the right place on the accelerator the car shifts along no problem but I have never had to push down so much to accelerate, it is to me at least very noticeable. I'll give it a few more days and see how things go. I understand that the cats are a sealed unit so couldn't exactly be cleaned through. I was told today by the garage that the car was quite smokey on friday and it wasn't acceptable to give back to me in that condition. After 120 miles drive on the motorway yesterday with plenty of foot down experiments with the turbo I can honestly say that it's hugely less smokey that it ever has been in the 3 years I've owned it.

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2004 BMW X5 3.0D
1985 Porsche Turbo 930
2000 BMW 328i
1985 RS Turbo Series 1 (Concours)
1984 Escort XR3i