I'm new to testing the vacuum system. The engine I am working on is out of the car, I replaced all the vacuum lines and checked all the components with smoke and a vacuum tester but was still not able to hold a vacuum. Finally found leaks in the vacuum reservoir. I have another engine in pieces so tested the reservoir on that one and it had a leak in the same place. My friend Newart also had to replace his reservoir, so it seems to be a common problem.
Check post #49 in this thread.
Bought a 2000 Boxster S project.