I've had this vacuum week for awhile and I haven't been able to track it down. It causes a high-pitched whistle at idle. It cuts in and out....and seems to go away once I give it some gas. I replaced a bunch of hoses and some of the plastic ones - I went to rubber ones. I've sprayed starting fluid around the throttle body, on the hoses, etc. -> with no help to the source.
The IAC was replaced and the egr valve more recently. Could it possibly be the EGR solenoid? I ask this because one time my dad unplugged the hose to the egr valve....it went away. But, then it would not do it anymore consistently - it didn't seem to work there after. The other options I was considering is something to do with the throttle body and I have heard of the intake manifold leaking - could cause it. Any ideas?

 

It definatly sounds like a vac leak. Use the old heater hose stethescope method and see if you can isolate where it is coming from. Sometimes theyre small and hard to track down.

 

I have the EXACT same problem as you do.the whistle only comes on when i barely press on the throttle. I `m almost positive that it is either an intake leak or my throttle shaft needs brass bushings.

 

i had a whistling noise too and replaced the intake manifold but i havent gotten it al back together yet, ill let u know if it fixes the problem

 

nope didnt fix the problem...
im pretty sure the "hissing" noise is just coming from the opening in the TBI..

i used a lenght of tube to listen and i only heard the noise when the tube was pointed to the opening of the TBI...

also, if i cover the oepning with a rag the hissing subsides..

and the hissing goes away as the car warms up and the idle drops.. so i think the hissing is normal.....

i still have a high idle, but i checked the vac and its at 19hg.. so i think that its safe to say that i dont have a vac leak causing the high idle... process of elimination, only, i dont know what to point the finger at now haha.. but yeah intake manifold is a no-go for the hissing problem, at least for me.

 

try checking the elbow on the front of the tbi unit that goes to the pcv valve. it will be really loud at idle but when you get on the gas the vaccum drops quite a bit. depending on throttle position.

 

i get the hissing when the motor is cold as well.... a lot more noticeable with a cowl hood and open element filter though

 

go run outside and check that little elbow real quick. i had the same problem on the 4.3 in my old truck. took me forever to figure out. when it was at low engine speed it would suck that elbow flat and create the tiny gap that caused the whistleing sound.