I am new to the list and an owner of a '83 240D. Love it, but am having some minor issues, including just replaced the thermostat. It's amazing how much better then engine runs when it is warmed up to 80C. Next up, my door locks.

I understand many things on a '83 240D work via vacuum. What is the LIKELY cause and solution to my door locks not working? Specifically, when I lock the car the locks do not lock. The lock problem arose gradually and is accompanied intermittently by the engine not shutting off when the key is turned to 'off'.

Doubtless this question has been covered in this or another forum, but I was unable to find such coverage based on a couple of searches. Thanks in advance for helpful suggestions, particularly where to look specfically for what I suspect may be vacuum leaks AT, IN, or NEAR the lock mechanisms in each door?

Best, Dan

Both caused by vacuum leaks. The door/trunk/gas flap locks all operate off vacuum, and a continuing air supply to the engine (via leaks in the vacuum system) keep the engine running.

Probably not both caused by the same leak, but rather a set of leaks, some in the engine compartment and some in the cabin.

You need to buy a mini-vac, then find a vacuum diagram for your car and start testing.
The vacuum pump assuming that it works provides a vacuum to the brake booster then has feed lines usually from the main vacuum line to provide vaccum

To the IP shutoff level via the key switch
To the transmission to modulate shift pattern
To the locks.

The rubber connectors that connect all this piping together is prone to cracking over 30 years of life and heat, plus of course handling, disconnecting etc. Plus of course the rubber in the actuators which are in the IP, and each door, trunk, gas door.

If you've knocked say the line providing vacuum to the transmission loose this can cause enough leakage to prevent proper shutdown and lock actuating.

This assumes of course your vacuum pump which does wear out is actually producing enough vacuum.