I have been trying to solve a similar problem on my 1989 300se. I have the rough idle/ low vacuum problem in my car. It begins soon after starting and it always clears up once the engine temp reaches about 70. In addition to the rough idle during this time period the car has little power and wont accelerate to highway speed until the engine temp reaches 70. Then it surges a few times and breaks out of it. After that it runs just fine. Like yourself I have replaced all the usual culprits and am trying to figure out what is not working right under pre-operating temperatures. Hopefully one of us figures it out or someone else has figured this out that can enlighten us.