170K is low mileage for that car. I have two, both over 280K, and they run very well. black smoke could be due to a clogged air filter, or a meddled with IP air filter is easy to fix. a meddled with IP can be impossible.
it concerns me that the PO only has 100 miles on the car. it appears to be in good condition, but you will need a lot of learning before you will be happy with this car. if it is cheap, (under 2000), and if it is not a necessary driver, I say get it. if the seller wants tons of money, pass. Lots of similar vehicles for sale without the problems this may have.
John

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!