You ever heard of a car "dieseling" ? That's what your car is doing....it's when the engine continues to run until all the gas is gone from the cylinders. That's normal....a diesel engine can easily get 250,000 miles, some can get 500,000 IF you change oil, filters regularly. If you're stomping on the gas and the turbo kicks in the Black Smoke is normal for any diesel when you're stomping/accelerating......
As for that "turbo-switch" answer I say <cough BS!> as you have this situation EVEN when your engine is COLD......plus there is no switch that continues to run the engine to cool the turbocharger, there's a switch to run the electric fans for radiators only.
International Harvester Trucks aka Navistar was one of the businesses in Ft. Wayne that produced diesel trucks....a diesel car is no different except for horsepower.