Exhaust gas recirculation -- meters exhaust into the intake to reduce flame temps and therefore nitrogen oxide emissions.

I don't know if you have one or not -- my 88 TE does not.

Classic stuck open failure is dying immediately on startup and exhaust gas in the intake (makeing "smoke"), and failure to idle unless the throttle is held open.

Non functioning exhaust valve will do the same thing, though -- I've never heard of a rocker breaking on an MB, but I suppose anything is possible.

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!