2000-high Pitched Hiss Coming From Engine Compartment - Toyota Corolla, Chevy Prizm (1998-2008)

Guest corollablackfox

I have a 2000, and its making a loud, high pitched hissing sound from the engine compartment. Only happens the AC is off. You can't hear it from the inside the cabin, only outside or obviously with the hood open. I've checked the pullys, changed the serpentine belt, nothing. It sounds like it's coming from the headers though. However, I could not find any leak in the gasket or in the actual intake pipes. We tried a few different things trying to find a leak, and nothing. I don't have an EGR valve, and we checked the vacuum tubes as well, and no leak there either. Is that just the sound that those headers make the air meets the fueluel?

Hello and welcom to the forums.

The picture you have in the link is of the intake manifold - the exhaust header is by the firewall side.

Can you get the hissing noise to change pitch by giving it more gas or putting the car in gear? I'm assuming that putting any load on the engine will reduce or get rid of the hissing noise, noise is just present when at idle.

Mine does this on occasion - sometimes cleaning the throttle body will help. But more than likely, you're just hearing the resonance of the intake charge in the intake manifold.

You can try the old school method of spray water around suspect vacuum leaks - around the vacuum hoses, fittings, around the throttle body, base of the intake manifold. If the noise changes pitch or stops - the part you just sprayed is the leak.

Could also be an exhaust leak - the donut between the exhaust down pipe and right infront of the catalytic converter tends to deteriorate quickly. If you noticed that the car seems to sound "different" when you drive through a puddle or during rainy weather - noise could be coming from the exhaust.

Also double check that the airbox lid is on tight - sometimes those rear tabs don't always want to go back in, and you might have the airbox lid cocked slighly open - that would also make for a hissing noise.

Guest corollablackfox

Intake Manifold, that's what I meant default_blink Anyways. Yeah, I tried the water test and all. It's deffinately not a vacuum toob leak. Now it doesn't really affect the performance, it's more just a nuisance really. I guess I could post a video of it tomorrow. Thanks!