That car has a thermostatically controlled additional air valve that operates when the engine is cold, common failed part. MB part number 000-141-03-25 with list of $202.

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MERCEDES Benz Master Guild Technician (6 TIMES)
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190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
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