Here are some pics of my E320's intake manifold vacuum connectors showing the circled nipple from your photo as the one going to the DM pressure sensor (B5/2) shown in pic 2.

The other nipple closer to the cylinder head has a Y connector going to both the fuel pressure regulator (40), and air injector (Y32) & EGR valve (Y27).

It's exactly how the diagram I posted above shows.








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