Well there is always another way around the barn. You car has a rather unique anti-dieseling solenoid that if functioning absolutely stops the problem.
What makes it unique is that the system is dead with the car running and activates at shut-off. The solenoid is the large round one one the bottom of the carb that is used for mixture adjustment. With no power (no connection) the thing is just the main jet of the carb. When the key is shut-off a relay powers the solenoid for about four seconds if I remember correctly.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician