You probably need a new shut-off valve -- it's a common enough problem. The part is inexpensive and attaches to the back of your injection pump.I am having a bit (A lot) of difficaulty turning off my 79 300 td. The ignition will not respond. I cant find the shut down lever. And disconnecting the battery does nothing. Any advice would be greatly appreciated.
It's probably not the pump, or your brakes would be suffering. It's more likely a vacuum leak somewhere else in the system, which can be really tedious to locate...I have a similar issue with my 83 300D. We've tried several used shutoff valves and they all seem to not work... what else can it be? I'm already assuming its the vacuum pump since the door locks are also screwey (weird acting). The brake booster works just fine though.