With 85k Miles, probably most parts which are common to fail are already replaced, unless it is on of the reasons the current owner is selling it. On a D1 you could be in for a water pump, a fuel pump, distribution cables, overhaul the steering pump, black smoke is an issue (could be the injectors or injection pump) but white smoke (after engine warm-up) means it is consuming your cooling water and that is engine overhaul. Most common defects are not as bad (windows do not open, not interlocking, dead battery, oil leaking at every joint) Verify the gear box, shifting problems occur sometimes when engine is cold at early stage and that means $$$$
D2 types are more electronically sensitive, which is bad as you have to count to much on your dealer or a good alternative.
A full diagnostic Test by the dealer or independent test center is worth the money before buying any car or truck.