Could be your coolant temp sensor that sends engine temp signal to ECU and ICU. If this signal is not correct, the air/fuel ratio is messed up. Maybe the ICU thinks your car is still cold and sends in more fuel than needed. I dont know where it may be located on your car, but you can ask people on FastLane or whoever your parts dealer is, try replacing it if you have not replaced it ever. For reference, on my 87, 260E, it is the last sensor on the engine, closest to the windshield, because there are more than one coollant temp sensor on my car and perhaps on your car too.

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Saumil S. Patel