Hi again,
There are actually two temperature sensors - one is for the Temperature gauge, and the second tells the fuel injection computer how warm the engine is. On a cold engine the second sensor "tells" the engine to run richer, and as the engine warms up the resistance of the sensor decreases, telling the engine to run leaner. My thought is that if you have a wiring harness short that decreases the temperature sensor input to a very low resistance value the engine will run very lean. What we need is some more input from more knowledgeable members regarding your engine that can identify the location of the sensor in question. Of course, if it's a short in the engine harness it might be harder to find, or go away, or become intermittent.

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Richard Wooldridge
'01 ML320
'82 300D 4.3L V6/T700R4 conversion
'82 380SL, '86 560SL engine/trans. installed
'79 450SL, digital servo update
'75 280C