Part throttle Air/Vacuum sound

[GTOSHO]

At very slight, initial throttle application, I am hearing an "air rushing" sound (kinda like keeeeeeeeeeeeeeh), that I suspect is either a vacuum leak or just the intake air through the airbox/Holley filter/MAF/throttle body, that I can hear inside the car particularly just after starting the car cold which is accompanied by a slight bog/hesitation and then after warm with no bog/hesitation but with a slight power surge. Apply throttle any more than this initial 1-10% and the situation disappears. It is somewhat intermittent, but with any climate controls on much more prevalent. It seems to be coming from the back, driver's side of the engine toward the front. I've checked codes over the past week and initially had 177/173 O2 rich, but after cleaning the MAF and throttle body I've not had those again nor any others. I've also replaced the throttle position sensor with no difference. The car basically runs very well besides this annoying issue. Any ideas/help would be greatly appreciated.

Tim - 94 MTX

 

[GTOSHO]

I guess I confused everyone?? How about simply, Is there a vacuum controlled device that actuates at part throttle that could be leaking? I'm not yet familiar with the whole of the vacuum system on these cars. I see what looks to be a diaphram with various vacuum lines attached just behind the radiator fan on the driver's side. What is its purpose?

 

[sdpatt]

If you have a vacuum leak, the large vacuum generated at idle speeds would make the leak quite apparent before you touch the throttle. If there have been any changes to the intake path upstream of the throttle plate, you are likely hearing the noises that the Ford induction system was designed to muffle.

 

[projectSHO89]

The easiest way to isolate the source of the noise is to eliminate suspects.

I would disconnect and plug individual vacuum lines from the intake and throttle body and see if any of them make a difference.

The IAB valve is computer-controlled and does serve to bypass the throttle plate in order to control idle speed and to perform the dashpot function of yester-years carbs.

Intake air noise is not a very common source of problems on these cars, I know I haven't experienced it and recall no previous inquiries since I've been working on these engines.

There should be a vacuum schematic on your emissions compliance label, if yours still exists.

Given that you have a slight surge, I would focus attention on the IAB, perhaps giving it a cleaning and see if that helps.

The only thing in the vicinity that you described that is vacuum operated is the canister purge valve and the carbon canister, neither of which are supposed to be "in circuit" during cold warmup cycle.

Steve

 

[Bluto]

Tim,
I have a 94 ATX. I hear the same damn thing.
If I just touch the accelerator, I hear it. I am not convinced its the sound of air. The sound goes away with just a little more pressure on the accelerator.

It sounds almost servo, or fluid like.

I am still hunting. Let me know if you figure it out.
-Bluto

 

[SHOBiz]

I get the same thing, a loud sound of rushing air when i first start up the car and let it idle. After the car warms up it stops but slight acceleration will bring back the noise. I have an aftermarket K@N cone airfilter fitted and i just figured it was just the sound you got without an airbox fitted to muffle the sound.

Mark

<small>[ February 04, 2003, 02:16 PM: Message edited by: SHOBiz ]</small>

 

[SuperG]

I have what I think sounds the same...it is loudest in the air filter box. In my case, I have a K&N Panel Filter and I removed the silencer cone. But I do not know what creates the sound...

 

[SHOBiz]

Bluto:
Tim,
I have a 94 ATX. I hear the same damn thing.
If I just touch the accelerator, I hear it. I am not convinced its the sound of air. The sound goes away with just a little more pressure on the accelerator.

Initialy after you rev the car the sound is loudest for a second because of a pressure drop in the air filter box/cone and intake hose to the TB, as the pressure evens out the sound lessens.
Thats my theory anyway.

Mark

 

[Mike Kopstain]

I have a custom intake on my car and for months I was trying to figure out what the **** this sound was when I started my engine. It sounded like the motor was sick or like there was oil starvation somewhere.

It turned out the sound was coming from the intake. When you start the vehicle (cold start) it is programmed to raise idle to warm up the catalytic converters. The noise would slowly fade away over about 1 minute. The reason it goes away when you tap the gas is because the comuter will drop the idle down to normal when the gas is tapped.

 

[Bluto]

Mark,
Not the case for me. This noise is there when the car is warm or cold. Again, its in park or driving. If the gas pedal has a tiny amount of pressure on it, you can hear it. Its very strange.

Good theory though thumbs_u

<small>[ February 04, 2003, 04:47 PM: Message edited by: Bluto ]</small>

 

[GTOSHO]

For my car, the sound is very noticable when starting the car cold and the idle is high as described. It fades away after a minute or so when the idle comes down some. When I touch the throttle when cold there is a drop in rpm or bog which might be explained by the computer returning to idle prior to increasing revs. Its still there when warm and while driving if I hit this throttle position I hear the noise and get a slight surge in power. From reading the postings, I'm thinking maybe the IAB is involved as well as the aftermarket filter and removed silencer. I plan to clean the IAB and try a stock filter as the Holley (K&N type) I have doesn't fit the best, the airbox top tabs are very hard to get into the slots and as a result it slides around alot.

 

[GTOSHO]

I'm still stumped on this. shrug The check engine light come on every so often when the car is cold and I've just started off driving, accompanied by this sound . I am getting codes of 173, 177, 542. It seems to be "switched" on and off by something. When I turn on the climate controls it makes it more pronounced. There is a vacuum line coming off the manifold right behind the throttle body that goes down to a gold cylindrical canister that looks to be a solenoid. Is this what activates the vacuum for the climate controls? Could a leak in one of these associated lines cause this noise accompanied by a rich condition as indicated by 173, 177 codes? How does the 542 fuel pump deal fit in?

<small>[ February 13, 2003, 08:10 PM: Message edited by: GTOSHO ]</small>

 

[shojuan]

Heh, I've had this sound ever since installing the SHO Shop CAI. I'll be damned if I can figure out exactly what causes it.

 

[Leon]

After enlarging the airbox cutout,removing the silencer cone and installing a K&N i had the same noise...i don`t think the IAB is involved as i serviced mine when i port and polished the intake,this was all done at the same time...the noise diminishes when the engine warms up..i can`t figure it out.....but it runs perfect!

 

[Bluto]

I think earlier in this post Scott hit it on the head. I have modded my Air intake. I have a feeling its just a sound that I need to live with.

I see Shojuan, and Leon are getting the same deal.

 

[GTOSHO]

Besides SHOJUAN with an '89 everyone else has a '93-'95. Any connection? shrug Regardless of whether the factory "silencer" has been modified, I'd be nice to understand what causes this. Like what was described, it is loud on startup and quiets as the car warms, but is still present at part throttle when warm (with accompanied slight power surge) and in my case is worse with climate controls on and may cause a rich condition. If I figure it out I'll be sure to post thumbs_u

<small>[ February 14, 2003, 08:44 PM: Message edited by: GTOSHO ]</small>