Engine Hissing/Vacuum Noise

[aontkos]

Hello all,

I replaced my valve cover gaskets about 400 miles ago. While I had the intake plenum apart I replaced the IAC, all intake gaskets, and vacuum hoses. I retightened everything to factory specs. The repair went well and the engine idles right at 600RPMs.

I didn't notice any noises immediately after the repair. I drove it about 200 miles on the highway and after exiting the highway and accelerating onto a side road I noticed the hissing sound. It sounds like intake noise, which leads me to believe it is a leak in the plenum or a vacuum hose that I have overlooked.

This sound only comes when I accelerate or manually open the throttle; it cannot be heard at idle or at a steady speed. I checked for loss/missing vacuum hoses and didn't find anything abnormal. I also tried spraying throttle body cleaner on vacuum hose connections and around the intake gaskets but there were no changes in RPMs. It sounds as if the sound is from the top of the engine on the driver side...it also seems to be louder towards the back.

Here's a video: https://youtu.be/LRej6C7gEqk

Any input is appreciated!

 

[Mellemel]

Mine does that. I think it's normal. did it not do it prior to what you did ? I don't think you have anything to worry about.

 

[aontkos]

Mine does that. I think it's normal. did it not do it prior to what you did ? I don't think you have anything to worry about.

It did not do that prior to the valve cover gasket replacement. The noise is driving me nuts since I can hear it within the cabin.Thanks for the response.

 

[Mellemel]

When i recently flushed out my heater core I was under the hood operating the throttle same as you in the you tube vid while burping the system. My 97, V6 made the exact same noise. Are you sure you were just not aware of it before? I nearly drive myself nuts hearing noises on mine !

 

[aontkos]

Bump for morning shift.

 

[bugman-74]

Mine made the exact same "suck" noise, and after countless hours of trying to track down issues/leaks, I have come to the conclusion that it is normal. It is much less noticeable now that I have the TRD S/C installed, so that is one possible solution path for ya :bounce:

 

[catrains]

When the engine is idling you have high vacuum. as you open the TP the vacuum increases in the air pipe . I would check that the intake air pipes to the TB are secure.

if you have an intake or vacuum leak the fuel trims will be high positive. should be +/- 5 .........normal reading.
when doing the intake gaskets best use bolts with the heads cut off so when you set it down it seats perfect. many have messed up this intake gasket work... I would also use perfect seal product .

 

[aontkos]

Thanks for the insight everyone. It seems as if the consensus is to accept the noise. Perhaps my high idle prior to the IAC replacement made the sound less noticeable.

 

[Jdecesare]

I know this is an older thread, but I am having the same issue as you. I replaced the IAC, all intake gaskets, cleaned and replaced the gasket on the Throttle Body, and ensured all and vacuum hoses are set. I retightened everything to factory specs. The repair went well and the engine idles right at 600RPMs.

I still am hearing an "air escaping hissing" sound, which to me would suspect a vacuum leak. However, after spending 3 hours and 2 cans of break cleaner later, spraying around around the intake, hoses, gaskets, valve cover gasket, PVC, pretty much the entire engine - didn't get any reaction from the engine. I also only hear this at idle and seems goes away once the throttle is open.

Here is the hissing sound I am hearing right near the throttle body . Does anyone have any suggestions? Thanks!

YouTube Link: Vacuum noise coming from Throttle Body - YouTube

 

[gamefreakgc]

I agree, that doesn't sound right. Do you have the throttle body gasket on upside down?

 

[Bad Luck]

What intake are you using? Was the noise present before working on it? Did you replace any other parts?

 

[mtbtim]

What intake are you using? Was the noise present before working on it? Did you replace any other parts?

I was thinking the same thing. That intake is definitely aftermarket, like the one Airaid makes, and they are WAY louder than the OEM air tubes that have the resonator box.

 

[Jdecesare]

I agree, that doesn't sound right. Do you have the throttle body gasket on upside down?

Fair question, but no I don't believe so. The gasket is in the same orientation and direction as it was previously. Using the same brand gasket as well - Felpro - Fuel Injection Throttle Body Mounting Gasket (Part No. 61038)

 

[Jdecesare]

I was thinking the same thing. That intake is definitely aftermarket, like the one Airaid makes, and they are WAY louder than the OEM air tubes that have the resonator box.

Yes - the intake is an aftermarket one. However it is the same one that has been on the car for the past 100k miles. I also regularly clean it with maintenance along with the MAF.

 

[Jdecesare]

What intake are you using? Was the noise present before working on it? Did you replace any other parts?

I cant remember the name exactly of the intake, but yes it is aftermarket and have on the car for 2 years now without issue. The noise did not exist until after I have cleaner my throttle body (was a tad dirty) and MAF after reading a P0172 - running rich in bank 1 code. After cleaning and MAF, TB, and replacing the gasket - I don't have the check engine light on/code anymore, but have noticed the air leaking sound as head in my attached video.

Even after doing a smoke test today - still not finding any leaks, and mpg steadily drops at idle according to the Scan-gauge. Another thing that didn't happen previously.

 

[mtbtim]

Yes - the intake is an aftermarket one. However it is the same one that has been on the car for the past 100k miles. I also regularly clean it with maintenance along with the MAF.

I think you just have to reverse some of your work to take a closer look at what could be causing the vacuum leak. Remove the air tube and remove the plenums so you can get a better analysis of your work and what could be wrong.

There is an air hose that connects to the IAC. That is the air assist hose that provides air to the injectors. Did you remember to connect that hose?

 

[Jdecesare]

I think you just have to reverse some of your work to take a closer look at what could be causing the vacuum leak. Remove the air tube and remove the plenums so you can get a better analysis of your work and what could be wrong.

There is an air hose that connects to the IAC. That is the air assist hose that provides air to the injectors. Did you remember to connect that hose?

Thanks Tim, that is a great idea and one I have been doing. I went back last night, removed the intake, and even the throttle body again (got a few new Felpro gaskets for it) - I checked the coolant tubes, air hose that goes to the injectors as you recommended, and everything is in place and didn't see/hear any leaks on the tubes themselves.

I also got a metal Manhole TB gasket - so might try that just to test.