Not that I have a diesel, but not uncommon as far as I know.
The solenoid is one possibility.
But also it could be build up of carbon in the cylinders. A problem that can come up when you use the car a lot on short trips. The old-fashion (traditional) solution is to bring the car on a long trip and give the engine some work to do. (German Autobahn comes to mind). (Don't use the M4, that's 50 most of the time !)
Alternatively there are cleaning fluids that you mix with the fuel (diesel)