I have an '82 240D. While replacing the air filter, I noticed that the opening for the intake has a throttle plate similar to what you would find on a carburator; it opens and closes with the movement of the throttle. I always thought that diesels didn't operate with throttle plates and engine power was regulated with the amount of fuel injected into the cylinders. It would seem to me that this is a restriction of airflow into the intake manifold. What am I missing?

Herb
'82 240D
112,000 miles