Aud A4 tdi turbo. lose of vacuum

Are you referring to the brake vacuum system, or do you mean something else?

I'd imagine that's it, there's precious little vacuum elsewhere on a diesel. There's a cam-driven vacuum pump that may have failed.

All that he has said is that the turbo is now working ok but it was the lose of vacuum in the first place that caused it to carbon up.So it must be the engine vacuum

its the engine vacuum system that operates the engine turbo

I'm sorry but you've lost me there. The prime mover for the turbo is the engine exhaust gases which spin a rotor and compress air by means of vanes connected to the same shaft as the power turbine. In my basic knowledge of these turbo systems there is also a dump valve which allows excessive pressurised air to escape - but no vacuum. In fact there is such a shortage of vacuum associated with a diesel engine that a vacuum pump has to be installed, often driven from the engine camshaft, to provide vacuum for the braking system - as already stated by Mr Bartam.

Diesels and vacuum are anathema and do not exist in the same universe.

Perhaps an explanation of the symptoms you originally experienced may help?