I've got a 1982 240d that I've owned for a few months. Initially I suspected a very small vacuum leak as I could only actuate the lock within 30 seconds of turning the car off. Eventually this time decreased and the passenger side rear lock stopped working altogether. Soon after this, normal engine shutoff failed and I have to cut off fuel at the engine every time. Now none of the doors will be locked or unlocked with the central system.
I've seen the diagrams posted in forums here but they do little to help with troubleshooting for someone with little enough experience to not know how this system really works, where the components really are, and just the best way to get to them all.
Is there any hope or help for me?
Thanks much. MF

Step 1. Go buy yourself a Mityvac. Don't argue, just do it. Mine was a whopping $26 at AutoZone.

Then read this post on how the 240D vacuum system works.
http://www.peachparts.com/shopforum/showpost.php?p=428715&postcount=7

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Rick Miley
2014 Tesla Model S
2018 Tesla Model 3
2017 Nissan LEAF
Former MB: 99 E300, 86 190E 2.3, 87 300E, 80 240D, 82 204D Euro
Chain Elongation References

If you have a Harbor Freight in your area, a mityvac is like $20. I gave up trying to get my locks to work correctly, and therefore eliminated it. It makes things a lot easier to troubleshoot vac-wise.

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1989 300E 144K

Get the mighty vac. A good book is from **************.com for trouble shooting. Took me all summer on and off to repair my door locks. Turns out it was a broken vacuum line. Also some good diagrams right from the forum here.

Be methotical, draw scetches, keep and do not throw out your notes. Take your time. You will learn your vacuum system for sure.

Tom Scordato
1977 300D
1979 240D