‘80 300SD…Engine Turn Off Problem
 

Engine won’t turn off with key. Have to go under hood and use manual shut off lever. What’s the fix and what parts do I need to get?

thanks
Bill

Check for leaks in your vacuum system... either T fittings, lines, or the actual vacuum pump....

Use the search function. This problem has been covered hundreds of times

You have a vacuum leak in the system somewhere. Time to get a mity vac and start tracking down leaks, and looking for cracked rubber vac connectors.

BTW, why all the bold and giant text?

Yep, it should be covered in other posts. Same thing was happening to my 1979 300SD and it was the fuel shut off valve located at the back of the injection pump. The diaphragm ruptured and oil got into the vacuum lines and made its way into the ignition switch. It's a good idea to clean or replace the vacuum lines going to the ignition switch after replacing the shut off valve.