New to the forums - I have a 2004 Jetta TDI.

I am now looking at buying a 1987 300D - with an OM603 engine.

The engine seems a bit rough at idle (I had looked at another SDL, with same inline-6 engine, and it was much smoother). There is a boop-boop-boop at the exhaust. Black smoke at start up. No visible smoke at idle. What appears to be mild black smoke when driven away (wish I had more time to check the smoke....).

I did the loose oil cap blow-by test. Nothing. Cap sits, doesn't even rattle. The head is a "16", not the notorious "14". Upper radiator hose has no significant pressure, even with engine warm. No oil in coolant. No oil leakage around head (Plenty of oil way down below though).

The original recalled trap oxidizer was just changed about 5 years ago.

Question is: what's the likeliest issue?

Would this likeliest be bad injectors? Bad Injection pump?

If its strictly a fuel system issue, I'd probably buy the car - can get for $2,500, which seems ok for an otherwise reasonably good condition 87 300d.

If the issue might be in the cylinders - then, I don't want to touch it.

For the same money, I can get a 1985 300D in great condition. But, the 87 300D seems to be a better overall design.