ok so were on the intake manifold and does that causes it to hiss?
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1999 Mazda 626 Question: ilden bad
Answer #1patrick mannion from Greg Solow's Engine Room, July 10, 2009, 00:09Master
The hissing sound is most likely a vacuum leak, was all the old gasket removed prior to refitting the new gasket? Again try pouring a little engine oi where you hear the hissing sound with the engine running, if the oil gets sucked into the engine and the engine briefly runs smooth you have a leak from the gasket..
With the engine running you may hear a slight "hiss" which is fuel running in the fuel rail.