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The engine is a huge vacuum pump. With any restriction in the intake, a significant vacuum will be 'pulled' in the intake manifold. That restriction is a nearly closed throttle valve during idling conditions, or a small opening throttle during cruise conditions. However, the airflow meter is located ahead of the throttle plate, and the metering flap should offer only minimal restriction. You will find very little to hold a vacuum at that point. Any hoses feeding to the rubbery airflow meter plenum will be air supply hoses, not vacuum hoses. Vacuum 'supply' hoses will attach to the intake manifold casting, AFTER the throttle valve.
Steve
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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7
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