So last night I was doing a pull and towards the top of 3rd, I hear what sounds like a garden hose spraying water ,but 10x louder. Let off the gas, all is well, drive it home. Open the hood, found vacuum line that runs to the top of my turbo smart valves (VTA), came off from the "T". Plugged back in and did 2 runs. Boost held 25+psi with no problems. Question is, what exactly does that vacuum line do ? How does it hold boost with it attached, but not when its off ? I would assume there is a diaphragm inside, but how would that help the car hold boost ? I thought maybe a coupler gave but when I saw the hose, I decided to attach and try that before tearing everything apart. All went back to normal but I want to know why it works the way it does.