I got a feeling this is being caused from the IAC,it is a extremly loud hissing, is it doing this for cold start higher idle, if so why doesn't my cars idle go higher for cold starts, it only does this when cold then goes away after a few minutes, am I dealing with a plugged IAC bypass, Ive cleaned the throttle body but it still does this, are there air passages in the plenum that could be plugged, its a 90 tpi with speed density

 

it is possible the IAC park postion has a worn spot. on gm the park
postion is usually 160 and the IAC may have a worn spot and can
not clear the spot.
using a scanner, you should be able to command and lower postion
and see if this clears the issue. if not, look into a ECT sensor or
rick O2 sensor.
airdeano

 

possibly a vacuum leak. if u wanan test for leaks,get some propane, witht eh car running,let a litle bit go around all the gaskets and vacuum lines. since propane is heavier, it will set around the manifold...if theirs a leak,the idle will jump up a little.

 

camaro, the noise is IAC related

 

alright,i ithink i mis read it,i thought it was coming from the intake manifold,not the intake tube.