Had same problem in a 1986 190D. Could not open windows or sunroof without sucking in diesel fumes. Spent way to much time looking for exhaust leaks and openings into the cabin. Exhaust smell was strongest in the trunk. Between the taillights there is a panel that hides trunk latch, wires, etc. Also hiding here are two one-way flapper valves that allow air exit (such as when slamming the trunk) but not entry. They snap into the bottom sheet metal that opens below the bumper. Found one just laying there. Cleaned up the minor soot, snapped it back in, found heaven. No more smell, can drive with windows open, sunroof open. Only "problem" is that #1 son turned 16, so of course, it now sports a stereo that can be heard way over the diesel, plus the interior glows with blue neon. The proplem is not the stereo, but whats on it. Pop in a Who CD and all is well. :-)

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Hanno
'79 6.9 Sold (after 27 years)
'83 280SL, 5 spd.
'94 E320 Sdn. 5 spd conversion
'02 E320 Sdn.(on loan to mom!)
'87 300E (5 spd. conversion) Sold
'05 E500 Wagon