Hi--

I've been experiencing similar issues.

When I took my exhaust apart two weeks ago, the header pipe had a black carbon coating inside. The O2 sensor and tailpipe also have carbon soot on them.

Any suggestions on why this might be happening on a 1990 240 that was built without an EGR Valve? Car has recently had a tune up, the air box thermostat is working, and the FPR valve is fairly new. Also, all of the hoses are in good shape.

Thanks for your ideas.
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If it needs to be maintained, repaired or replaced on a 1990 240, I've probably done it. '90 240DL, 255K looking forward to 300K badge (or sticker??). >>You haven't really worked on a car until you draw blood<< :-}