call the dealer and ask for a KEY CODE for an 84 318i, if they still have that information, i think the key codes are only stored for the past 10 years, for ford its 5 years,
if they dont have a key code, youll need to replace the lock with a new one from BMW and since this is an old ass car they might not even have a new key lock for it and youll have to find one at a junk yard