Check all hoses and connections for tightness.
If theres a bad split someplace, use a can of carb cleaner/brake spray and spray each joint in turn with the engine running.
Any air leaks will show up as a rise in rpms which drop down to normal afterwards.
Dont go mad with it tho else you may set the car on fire.....
Can only be in the induction air path so basically any hose or connection that is on the pressure side of the turbo ( including the intake manifold) is subjected to boost which can bleed off if theres a leak at all.