Not sure if these are what your problems are, but here are 2 things on my 81 300d that I just took care of, and has to do with your symptoms.

1st are the vacuum lines under the hood that come out of the firewall near the oil filter canister. Whenever I change the oil in my car, or mess around in this area I always by accident pull the green hose loose, and the car wont shut off. The green one is a little loose on my car, so it is the one that gets pulled out easily.

2nd I just repaired a fuel leak in my car, because I noticed my gas mileage was very low and I also noticed a large pool of diesel on the ground when I came out from the grocery store. It took some searching to find the source, but eventually saw it was right in front of me. The fuel line that goes between each injector(the braided stuff) was leaking on the injector all the way in back, #5. I actually had some of this hose because I just replaced it on another 300d.

These are 2 things to easily check