Anyone have the vacuum diagram for a W202 C280 (center vent is inop)

Hello. I am trying to track down an apparent common problem in my US-based '97 C280: the center vent doesn't always flow air, and has a lot to do with throttle position / RPM.

From what I can tell, it's vacuum related, but I need to know where all the lines go to, such as a distribution block in the firewall, etc.

If you have a vacuum diagram available, please let me know!

Thanks in advance.