Hi, first I can't speak english, so I apologize if I won't be enaugh clear.
The biggest problem with 20v turbo is engine.
First you should change the cam belt even if it has just been changed, do you really trust in job made from an unknown people?
Then you should check turbo: at minimum rpm you shouldn't see blue smoke from exhaust (it means turbo has got problems).
You shouldn't hear metallic noises from engine (like hammer), this means there is something wrong with phase variator.
Of course, you should drive by your own the car before buy it, to "feel" if the turbo works correctly.
Better if there is a manometer embedded: a common trouble is the turbine (peak 1,2 bar, average 1 bar) doesn't reaches full pressure.
You have just to chenge the pierburg valve or use a boost controller.
It could be also the waste-gate valve.
But even the turbo works correctly, keep in mind in the future to change it for safety.
