For my new-to-me 190D turbo, the engine has an odd surging to it. It's very similar to surging from a cruise control, but this happens without the cruise engaged or even attached. It seems to happen mostly at higher rpms.

It's like the engine cuts out and then cuts in again.

I'm wondering if the turbo is cutting out (but I'm totally ignorant of turbos--do they always operate or is there some control?). In doing some reading, I'm suspecting the overboost protection valve or the turbo waste gate, but I'm not clear if failures could be intermittent like on my engine.

Any thoughts? Suggestions? (Remember, I don't know much about turbo operations.)