Date registered: Sep 2016
Vehicle: 1982 300D Turbodiesel (US Spec)
Location: Costa Rica
Mentioned: 1 Post(s)
Quoted: 20 Post(s)
I am not sure, but I think you might be a little confused. There is not such thing as a “VCV shutoff valve”. There is the shutoff valve and the VCV valve, and they are different things. The VCV valve controls the amount of vacuum that goes to the vacuum modulator according to the throttle position.
As far as I understand, the VCV valve doesn’t hold vacuum, in fact it was designed to leak a certain amount of vacuum depending of the throttle position and requires a specific procedure to test it.
By your description, the shutoff valve is partially shot, it should hold vacuum. If you are going to replace the shutoff valve, please carefully read the instructions on how to do it because if you install it in the wrong position, the engine will run away.
Also, that faulty defrost pod or any other leaky pod in the dash can make engine shutoff slowly if the climate control is running.