When I unlock the drivers side door none of the other locks open. I have to manually unlock all the doors. When I use the key on the drivers side, I hear a noise (probally vacuum pump) in the trunk for about 10-15 seconds. Nothing happens. I know it's all related to the vacuum system, how do I isolate this problem to the cause? Thanks again for all the help.

1982 240D 225,000
1983 300DT 175,000
1983 300DT 160,000 great car
1986 300SDL problem child

In The Same Boat...
 

I have the same problem on my '82 300SD! I was told that there is a leak somewhere in the vacuum system that controls the doors, trunk, and fuel door locks. I checked the vacuum/pressure pump (it's in the trunk to the right rear of the spare), and it works fine. The leak is somewhere in the tubing that makes it all work, or in the doors where the vacuum meets the actuators. Bottom line. Are you savvy enough to diagnose it on you own? Do you have a presure/vacuum pump with a guage on it? Does it really mean that much to you? Can you afford to have a local shop diagnose and fix it for you?

These are the questions you need to ask yourself, along with the "Why didn't I already search the archives for an answer?" question. I haven't found it to be such an issue that I have actually done an archive search before now, but now that you have reminded me...