That is EXACTLY what that idle solenoid is for--anti diesel. It simply connects to "ignition run" so is energized "with the key." It does not have enough "pull" to pop the throttle open, you have to bump the gas to get it "up." You set the "curb idle" on the solenoid, and then when you kill the key, the throttle blades close a bit more. This was done especially with the slow curve/ retarded timing "back then." You can "lessen" this if you run a fair amount of initial timing advance.
