Martin
So the flap has a spring to hold it open and the vac pulls it shut at ign. off, or it should do. You need to test the solinoid now.
But as Alan Kane has posted before you will always struggle with-out the right test equipment, and too be honest a mity-vac is one of the most basic,s of must have,s. If you aim to continue in the trade you will have to spend BIG, you wasting far too much time with-out correct equipment and training.
I will have another look for info on this, but this is a bit old for my nissan info.
Kev.