R45 suspected vacuum leak

Ok so just a quick one. I suspect a vacuum leak so trying to narrow it down, i pulled the small air pipe that runs from the IAV to the intake duct for idling, stuck my finger in the pipe to plug it, now surely that should make the car stall? Afterall not enough air can get in through the throttle body as its closed (hense the need for the IAV in the first place) i have tried a smoke test, although this was hardly the correct procedure, i just blew some cigar smoke down the pipe a few times but i can see nothing leaking out from anywhere.

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