Have you had the system cleaned out before?
The D5 needs a big clean in a shop that knows , the swirl flaps need to be checked , their motor and arm sorted and reset in the computer , its a dirty dirty job for them to do but so good for the engine!
YOU MUST DRIVE IT LIKE YOU STOLE IT at least once a fortnight , preferably all the time , never and i mean NEVER sit and warm it up , just DRIVE or you block it up with horrible crud from horrible DIEsel fuel