You definitely do not want to hear an air 'hiss' of any kind from any of the vacuum lines. I would fix this leak, and hope that's the only problem. A vacuum leak can certainly cause erratic, rough idling.
95 Contour Zetec, ATX (wrecked, sitting in the barn)
95 Mystique Zetec, MTX
2000 Taurus SEL 3.0L Duratec
1994 Crown Victoria LX 4.6 V8
1993 Chevy Silverado 4.3 V6
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