My 300D is a rocket compared to my 300TD...so, after a fashion, I've been fighting this same issue for a year, doing all the same things recommended here with no significant improvements. But, I think I'm finally on to something. Do a search of the diesel forum for the following: "near dead miss at idle", "psfred" and "pressure valve holder seal ".
Or go here:
Near-dead miss at idle
Good luck!