Sighing sound - noticeable noise at air intake?? when turning off

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rgnjc
Posts: 66
Joined: Sun Sep 11, 2011 12:53 pm

Sighing sound - noticeable noise at air intake?? when turning off

Post by rgnjc »

I have a 2005 AWD Vibe that is making a sighing (almost hissing) sound when I turn the engine off. I believe the sound is there when its running, but its really only noticeable when the engine turns off. It may be located towards the top end of the engine, and using a mechanics stethoscope (I'm a newbie so this is my first time using one) it seems I can hear the sound when listening directly to the air intake. I tried other components to see if it was a pulley and I could not hear it, nor could I hear it when I listened to the bottom internals or the valve cover. Does this sound familiar? Is this normal and I just haven't noticed before? For the most part the car drives well, though it seems to not start as strongly as it once did. I replaced the plugs this weekend because they were long overdue and they were well worn (gap was over 2x what it should have been).

My car goes to AAMCO next week for a tranny related issue, so they said they will take a look. In the mean time though if its something I can identify and fix myself I'd rather do that. I will post a video of this issue. There may be some squeaking in the video that is related to my flex plate (getting replaced next week) but the video shows start up and then turning off. When the car turns off its the last sound you can hear.

Possible issues: air intake manifold, maybe a valve issue? Perhaps a bearing issue?

https://youtu.be/WSGJj1oYtg0
2005 Vibe base AWD w/ M&T, 191k miles (as of 8/2022)
2007 Vibe base FWS w/ M&T, 150k miles (as of 8/2022)
Bookworm
Posts: 764
Joined: Fri Nov 05, 2010 11:21 am
Location: Houston, TX

Re: Sighing sound - noticeable noise at air intake?? when turning off

Post by Bookworm »

Usually a sighing or hissing noise is a vacuum leak somewhere.
rgnjc
Posts: 66
Joined: Sun Sep 11, 2011 12:53 pm

Re: Sighing sound - noticeable noise at air intake?? when turning off

Post by rgnjc »

Did an inspection of all the hoses and vacuum solenoids today to the best of my ability and everything seemed to be sealed up tight!

I tried spraying some carb cleaner on the air intake manifold to see if any would get sucked in and affect the idle speed. This test indicated no leaks. However, I then tried some windex and got a different result. In one area of the air intake manifold gasket there were bubbles coming out indicating an air leak! I thought this was strange because I expected air to be drawn into the manifold if there was a leaky air intake gasket. I pulled the air intake manifold off and the gasket is as flat as can be and I can't even feel the gasket seated in the manifold. I will replace the gasket tomorrow and see if the issue is resolved and I'll update with some pictures of it then.

Also, I got to see my valves and they look surprisingly brand new for 153k miles. They barely had any deposits after running a full can of seafoam spray through the intake the other day. I don't know what they looked like beforehand unfortunately, but knowing they're clean now is assuring!
2005 Vibe base AWD w/ M&T, 191k miles (as of 8/2022)
2007 Vibe base FWS w/ M&T, 150k miles (as of 8/2022)
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