Vacuum lock problem
 

When I pull my driver side lock pin from inside it doesn't open all the other locks. Instead I hear the vacuum pump churning away for about a minute.

If I use the key it closes and opens the door and all the doors with no problem from the drivers side.

If all the locks are open and I push my drivers side pin down it closes all the locks but I can hear the pump churning again for a minute after.

Where should I start looking.

Its a W124 260E 1988. Doh!

I checked the pump in the back but I can't see any loose connections. I'm going to get a vaccuum tester.

checkt he fuel door vacuum lock...

Mine was leaking so I capped it off temporarily

I'll take a look Ashman. You might be right, I don't think I hear the clunk from there anymore. Thanks for the response.

I had the same symptoms up until 2 days ago. In addition to erratic lock behavior, I could also hear a hissing of air in the trunk.
Turns out that a vacuum line needed a bit of rubber tubing. A 1 inch section had rubbed trough, or was possible eaten through by acid when my battery exploded a while back.