Does this car have a coolant temperature sensor (also called fuel injection temperature sensor) ? If it does check this one also. This will be a resistance check, 2.5 to 3.5K when cold and 250-350 ohms when engine at 80 deg C. On my 87 260E, this is the last sensor on the engine, towards the windshield. This sensor informs the computer about the temperature and the computer adjusts the air/fuel ratio accordingly. If the resistance does not drop by a factor of 8 to 10 when temp changes from 20 degC to 80 degC, replace the sensor.

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Saumil S. Patel