Coolant temperature sensor is my bet. It's the two-pronged sensor near the very back of the cylinder head on the driver's side (assuming LHD). It has two seperate wires on it. One wire goes to the fuel ECU, the other to the ignition module. Fuel is much more sensitive. Both terminals should have some resistance to ground. If one side is open to ground, try switching wires as a temporary fix. About $48 from fastlane.

JFYI, the single terminal sensor is for the dashboard gauge and the three pin jobby is for the radiator fans.

After that, search for the thread on adjusting the EHA. Many contributors to fixing exactly this problem. I learned on my 260E, very similar.

Best of luck,

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Norm in NJ
Next oil change at 230,000miles