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Silent "Ssssss..." from the firewall

1K views 8 replies 7 participants last post by  ppp111 
#1 ·
In ca 75% of cases when during driving I release the gas pedal (eg before traffic lights) I hear a clear (and not very loud) "Ssssss" somewhere from front - close to firewall. Like in front of me. It lasts ca 1 to 2 seconds. What can it be?

Otherwise the car runs fine.

Can be any air that goes away in this particular "releasing the gas pedal" situation? Or maybe it also happens when normally driving, but I cannot spot it, as cannot be heard when more noise is around. But for sure is associated with releasing the pedal.
 
#2 ·
I think the Ssssss sound comes from your dome lights over head ,i just hit by my hand and its goes away ,i only hear it sometimes very low sound that i can not hear it when I'm driving ,why its happened i notes it after i changed the lights but have no idea why its happened.
 
#3 ·
sounds like freon travelling to/from evap. a bit like gurgling sound?

its a wild goose chase tbh. the insulation will prevent you from hearing anything from the engine bay itself so that would be my guess here. should have no correlation with the gas pedal tho
 
#4 ·
Check your brake booster and the vacuum connection between it and the inlet manifold;
 

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#6 ·
+1 on the brake booster theory. When you let off the gas and the throttle plates close engine vacuum climbs rapidly. Either the brake booster's diaphragm or one of the vacuum lines going to it has a leak. The hiss you hear is one of those components sucking in air.
 
#7 ·
Thank you. This booster theory (and vacuum aspects there etc) might make sense then - as per your descriptions. I will check.

But also just to be safe: and what can be the outcome if it stays like that? How does it affect, in brief, any action under the hood (performance, brakes)? Towards what would it deteriorate?
 
#8 ·
How does your car run in the mornings after its left cold over night? Do you get any sputtering? Any hesitation until you pop it up to 2000rpms or 60*C??
Ifyou do have this it's the vacuum lines from the secondary air pump system to the back of the engine.
I had this noise and its now gone since I replaced those

Sent from my SGH-T989 using AutoGuide.Com Free App
 
#9 ·
I was rather asking if this story also belongs kind of to the "leaking air hoses" group, and e.g. causes performance to not to be optimal. Maybe it can run even better if this hiss is removed, and I am not aware about this fact ! :)

It seems to have good power (with eg acceleration ca 6,3 in 0-60), but maybe the general responsiveness is affected or so and I do not even have a chance to know. That is why I am asking.
 
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