If this were to occur on my 87, 260E, I would check the idle control valve. It is an electronically controlled air valve. It has a coil which can be tested for resistance, across the valve you should get about 7 to 10 ohms. Also you can disconnect the connector and apply 12V to one pin on the valve and ground to another, you should hear a buzzing sound, if you dont, just replace that valve. I am not sure your car even has this component and where it would be located, but you can ask your mechanic about it.

__________________
Saumil S. Patel