Hello and welcome to the forum! Take a look at the link below to one of our site's DIY tech articles on vacuum issues. It should help you troubleshoot. Please let us know if you have any other questions or if we can assist with any part needs in the future.

https://www.pelicanparts.com/techarticles/Mercedes-Benz/09-ENGINE-Fixing_Common_Vacuum_Leaks/09-ENGINE-Fixing_Common_Vacuum_Leaks.htm