Good morning, I have a problem with a Ford Focus 1.6 tdci - cylinder 1560 - engine type G8DD - KW 80 - year 2010

The car occasionally goes into recovery with a drop in performance.

Switch the engine off and on again and for another 2-3 days the problem disappears.

Diagnosis [P0299 UNDERBOOST UNDERPOWERED TURBO BOOST]

Checked the integrity of the sleeves, pipes and pneumatic valve... everything seems OK... 

I have read in various forums that it is a problem that has been encountered many times but never solved.

Has it already happened to any of you? suggestions welcome