5.9 sucking air

[braap34]

i have a 2000 ram 1500 5.9 and yesterday when i started it after driving it most the day it started idling around 1300rpm. its normally around 700ish. i didnt think too much of it and ended up offroading later on and it didnt get any better nor worse. but today it started making a hissing sound like a lose air hose on a air compressor while running when im not on the gas. i pulled the airbox and the throttle body was pretty dirty so i gummed it out, but its still making the hissing sound. any ideas what is causing it? im thinking plenum gasket is leaking. its making the sound with the airbox off so it shouldnt be that. and the gasket is only two weeks old. also two weeks ago i installed a spectre high flow filter and since then it had a speratic idle from between 600-900rpm.

any help is appreciated! thanks

 

[HolyRamBatman]

Welcome to RF.

Sounds like a vacuum leak. If you can't find it by just looking and feeling for bad spots on hoses, get a 2' length of hose. About the size of a pencil. Put one end up to your ear and the other end move around the engine bay where you think the sound is coming from. The 2' piece of hose will act like a stethoscope and amplify the hissing sound when you get close to it. Old school but it works.

Good luck.

 

[jf5.9]

When we put a Cold air on my buddys fresh ported and polished 5.3 in a Chevy our hissing noise came from the throttle valve not closing all the way after you got off the throttle - the force of air coming into the throttle body jarred the valve to a degree - we tore it town and unstuck it and it was fine ever since - might be worth a look see if you don't find it anywhere else

 

[ramminator97]

My truck would start making loud hissing noises when I was at idle, it ended up being the upstream o2 sensor. The computer thought it was getting to much fuel and not enough air and started sucking in air to compensate. when it did this it woudl lean out and stall.

 

[1badass1500]

Mine was making a hissing noise and ended up being the lower intake gasket but also could be a vacuum leak.

 

[talon6]

any codes?

 

[dodge dude94]

You replaced the TB gasket when you pulled the TB, right? If not, that might be your vacuum leak right there. There is also a vacuum fitting on the TB going to the vapor canister purge crap. I have broken that hose before and had some weird stuff happen for a short while.

Also, do you have your little air box ring gasket? If not, that can also cause a hissing noise. My truck had a power-whistle for a while before I installed one. lol