Well, Steve might have something with that throttle switch even though the explanation needs some serious help.
The mixture while altered electronically by the EHA is always controlled by the airflow meter working on the fuel distributor. The airflow at idle is managed by a second small throttle (the idle air valve). The air that it lets into the motor still passes and is measured by the airflow meter.
The idle switch is a signal used by the idle controls to tell them that the throttle is closed and to go ahead and feedback control the idle (feedback control means that if the idle is too low it adds air, if too high it shuts down air... it reacts to the condition). One must realize that if the idle is too high the valve shuts down. If this were to occur as one drives (the speed is high so the valve is shut) then the valve would be shut when you rapidly realeased the throttle and the engine would die. When the system is off idle the controls hold the valve in a slightly larger setting waiting for idle again and time to control.
Another function of the idle switch is to tell the KE controller that one has released the throttle. If the rpms are high enough the the fuel control shuts down the mixture for something called decel cut-off.
I would monitor these controls and see which are varying during the event.
I would also watch current through the idle controller as the OVP relay can cause the current to go low and leave a very low idle.
Bosch Master, ASE Master, L1
33 years MB technician