Overboost 1.9tdi b5 Audi a4

Anyone have any ideas what could be causing overboost if I go over 3k revs the car will go into limp mode no boost but no eml light switch key off and on it will be ok till I go over 3k again. Or if I'm stationary and rev car it will chatter thru airbox then missfire and smoke quite badley. If I leave it for 5mins will start up ok. Iv scanned it with a boch kts diagnostic and its giving code 4626 boost control differance. Any advise would be great thanks.

Sent from my HTC One_M8 using Tapatalk

What engine code? It's likely turbo vanes or n75 valve