Usually on these diesels when they do not shut off it is due to a vacuum leak or a failure, of some sort, of the vacuum system. The ignition switch has vacuum routed to it and when the key is turned off it activates this part of the system and the vacuum shuts of the fuel supply to the injector pump. Perhaps you broke a vacuum line in the replacement, these lines become terribly brittle over time, or one became dislodged. A large leak can keep components from working properly. If this non stop problem was sudden and directly after you changed the starter, I would trace and inspect all vacuum lines in the area you worked in and perhaps the intire engine compartment. There are a few threads on this problem if you need more information. Good luck.

Rick