Not sure if this will help (I've never worked on the car you have), but my 95 E420's coolant temp sensor has decreasing resistance as the temperature gets hotter. If you short the contacts (I used a pair of needlenose pliers), the car thinks that the engine is hotter than it really is, and activates the electric cooling fans.

It sounds like your problem could be that the car thinks it's cooler than it really is. Try shorting the contacts and see if it fools the car into thinking it's hot, and reducing the idle to normal, non-startup (normal idle) mode.

Before you do this - someone please confirm that this won't fry something in the engine, and that an '82 temp sensor has the same inverse resistance with temperature that my 95 does.

Troy
1995 E420 89k