Hissing
 

99 lhs makes hissing noise when transmission is not in park or neutral brakes applied and in gear.
will also do it when cold or if you raise the idle then it just stops . havent found anything leaking yet . is this one problem or two???? thanks

has something to do with vacuum . can hear it under the hood cant tell where its coming from no lines are broke

found a couple of air leaks . a few o rings on fuel injectors and bottom bolt on throttle body was half way out . not sure what happened there gasket still looks good

got car all back together runs like new. still have like a sucking noise when cold till it warms up then its gone. then if you give any gas at all then the sucking noise for a few seconds then it stops . looking for ideas