It's worth making sure the idle contact switch on the linkage is connecting properly, and also I suppose the one in the throttle body too. The fact that there are 2 of these, plus 2 air temp sensors, 2 coolant temp sensors (4 if you count the fan switch and the dash guage) shows what nowadays we regard as a crazy system. At least Mercedes fitted it with failsafe 'default' modes, and seem to use high quality sensors and wiring that doesn't fail often. Broken wiring is not unheard of though so worth checking if those switches do work that the signal is repeated at the ECU connector end.

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190E's:
2.5-16v 1990 90,000m Astral Silver
2.0E 8v 1986 107,000m Black 2nd owner
http://www.maylane.demon.co.uk/190esmall.jpghttp://www.maylane.demon.co.uk/190esmall2.jpg