Just looked at my 400e...
I have two small boxes next to each other with vac hoses. I traced the main vac hoses and they appear to terminate on the top of my engine. 1 tube directly into the intake manifold and the other into a sensor or something screwed into the front of the intake manifold.
I haven't a clue what they are doing. Heck, my mechanic found a similar looking tube loose up next to my master cylinder and it turned out to have something to due with transmission shifting sensors ??????
Perhaps a more technically inclined reader will respond