If you have dirt in the manifold, you have a vac leak.

Sadly, what is probably leaking is the seals between the manifold halves (top and bottom), plus the plastic connector between the air flow meter and manifold can crack. Seals are cheap, but you need manifold gaskets too, and the pipe is costly.

I suspect the seals are shot, but you also need to check the power brake booster line and the other vac lines.

I would replace the injector seals, too. They don't go bad often, but yours are VERY old.

Correct mixture must be set with a CO meter on your car.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!