Well, shut my mouth!
It sounds like this is the newer version of the anti reversion valve. Or what exactly is it? And since it isn't for rpm control, why would it be called a throttle body?
People get hung up over semantics, but the basic design and assembly of it is just like the electronic throttles on VAG gas cars. If you set the 2 side by side, you could not really tell the difference.
On the PD diesels, the throttle (technically VAG calls it an 'intake manifold control flap') is primarily for EGR function and catalyst operation. On the CR cars, it is also used for DPF regeneration. Keep in mind the newer diesels run a 'richer' air/fuel ratio than the older ones.
The ECU closes the throttle some when the EGR valve gets opened, to force a higher flow (higher velocity) of EGR into the intake. That higher velocity along with proper ULSD fuel pretty much makes intake clogging a thing of the past. The PDs simply never gunked up intakes like the VE cars did.
It can also allow the engine to force a richer (higher fuel quantity) without pushing the RPMs/output/torque of the engine up, and that extra fuel helps to keep the catalyst hot under certain conditions. The PDs cannot do the post-combustion/exhaust cycle fuel injection like the CRs can, so the only way to get more fuel into the exhaust to keep the catalyst lit off is to increase the IQ. But as you know, in a diesel, if you increase fuel, you increase RPMs. To limit that RPM from going too high under these conditions, the throttle is closed some.
And of course it is used for anti-shudder function at engine shut-down.
There are other (older) diesels that actually use a throttle more like a gas car, that forces vacuum under the throttle plate which acts on a plunger that is directly attached to a fuel metering rod going to the pump. MB used such a system in their diesels for YEARS. It was very similar to a carburetor actually, where vacuum and airflow were employed to meter injected fuel quantities.
Then later MB diesels used them to help keep the engine quieter at lower RPMs (my 1975 240D was one such animal, the throttle plate in the intake manifold was directly mechanically attached to the accelerator pedal, along with the fuel metering lever on the pump).
If you stand next to a CR diesel idling, even with the hood up, (Sprinters especially), you will notice how darn quiet they are. Well, part of that is because CR engines can run the injection timing literally anywhere the ECU needs, and at idle they can be WAY retarded. That way retarded injection timing makes the exhaust catalyst(s) stay hot even at idle, makes the engine quieter, and when used with a throttle (which is partially closed on them at idle) makes the engine even quieter AND smoother because if the engine is not compressing all of the air it could be that high compression won't be being used as much.
For some reason, the myth that 'diesels don't have throttles' keeps on going, despite plenty of them that do use them in some capacity.
Bosch has an excellent book on EDC systems and how they operate, including throttled versions.