Grant, it does not require you to tell it when to turn off. That type of air valve was designed to work by itself independant of the ecu. It turns off based on the heat it sees on whatever you've bolted it to. when it gets up to temperature it throws a switch internally and turns off.
This is how they worked on all early bosch systems such as motronic. The fast air valve had nothing to do with the ecu. it is given power all the time and it turns itself on and off based on its temperature. try it.
that is why you are getting the situation you describe. ms is never going to have full control of this type of valve. If it were an on-off vacuum switch, temperature of the valve itself never matters, it is only based on water temp and ms can turn it on and off as it likes.. you are always going to have 2 situations where ms can't control the valve (ms cold, valve hot and ms hot, valve cold) as you basically have two on-off switches in your circuit.