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Discussion Starter #1
My car just developed a loud hissing sound and it is coming from the airbox.Someone mentioned the IAC.I ordered one and am going to install it tomorrow.I can't think of anything else it could be.BTW,car runs fine and no CEL.Anyone else ever have this happen to them?
 

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The IAC isn't close enough to the air box for you to think that it's coming from there. You could possibly have a hole in the box or it's not sealed right.
 

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Discussion Starter #3
I have been told that the sound resonates in the airbox.If I pull the upper part of the airbox up you can hear the hissing up in the intake tube.
 

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Discussion Starter #4
I just pulled the IAC off and tried to clean it.It was pretty dirty and there was some gunk in there that wouldn't come off.Made no difference in sound,hissing still there.It is pretty loud and you can hear it in the car with the windows down if you drive by a wall or another car.Very annoying.I am going to try the new IAC in the morning and see what happens.BTW,it seems to go away when you give it more than half throttle,that is what made me think it might be the IAC.
 

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sounds like a vacuum leak maybe it's coming from be hinde the intake manifold and echoes down the intake pipe
 

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I got a 95 V8 and for the longest time i thought my air box/tube was cracked or something. Till this day i get a HSSSSSSSSSSS....it's the pcv valve and hose, just sucking air.

I already changed it and some hose for good measure, and sound still there....you squeeze the hose, HSSSSS gone..
 

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broke else where more than one spot dose your car run no so swell?
 

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Discussion Starter #8
snow said:
I got a 95 V8 and for the longest time i thought my air box/tube was cracked or something. Till this day i get a HSSSSSSSSSSS....it's the pcv valve and hose, just sucking air.

I already changed it and some hose for good measure, and sound still there....you squeeze the hose, HSSSSS gone..
No,this hissing sound has gotten much louder in the last month or so.I have done nothing to the car that would make it do this.PCV valve is new as is the hose going to it.I understand that a little bit of sound from the airbox is normal but not like this.
 

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Discussion Starter #9
Ok,now after working on it for the last hour I am more confused.I put a new IAC on it and it made no difference.I also was wondering what that black box that is connected to the IAC is?The one that is in between the IAC and the air intake hose.I was thinking it was some sort of filter.I looked inside it and there is nothing in it,can see right through from one end to another.I wonder if it is some sort of silencer for the IAC inlet?Also found one of my intake bolts about halfway backed out.I tightened it but the noise is still there.It is clearly coming from the mass air.I wonder if the o-ring under the electronics is bad?I am going to try the mass air from my friend's car and see what happens.I am just scratching my head at this.
 

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Discussion Starter #12
razzibird said:
Is your air silencer removed?
Yes,the air silencer is removed.However,it has been removed since right after I bought the car(8 months ago) and the hissing has just now started.And the airbox is sealed just fine.
 

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Discussion Starter #15
I found the problem.It is the throttle body.I took the one off of the 2003 4.6 that I have that is waiting to go in the Tbird and the hissing went away.Only problem is that it won't idle right when in gear,it wants to stall when I put it in gear.But at least I have found the problem.I cleaned out everything on the throttle body but it still makes the hissing sound.I have swapped them out a few times back and forth and the stock throttle body hisses and the 2003 one does not.I think I am going to order a Ford Racing 70mm one and be done with it.I am glad I found it because it was driving me crazy.
 

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Discussion Starter #16
Well,my 70mm throttle body finally came in and I installed it today.I disconnected the battery last night to make sure all of the memory was erased.Today I installed the new throttle body and reconnected the battery.It idled perfect and most importantly,no hissing.I drove it around the block to make sure all was good and it runs and idles fine.Didn't really get on it so I don't know if it feels any faster.Now I need to go to the track and see if the catback,throttle body and mass air helped.I will be running it at Fun Ford Weekend in Orlando March 3rd,4th and 5th.
 
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