At the end of my rope! Intake whistle...

[1996XLT-68]

Regarding my 1996 XLT with 4.0 pushrod motor:

I've tried all the solutions posted to the board in regards to the intake whistle including cleaning the IACV, MAF and all that, but the whistling sound persists.

I'll try to describe the sound. It only occurs in gear and it is not a velocity-induced sound (I've gotten it to make the sound in drive with the parking brake on). It occurs under medium throttle in a very narrow band. It starts above the range of hearing and as you press the throttle down more, it descends until it goes away. It sounds like a turbo, but backwards (with turbos the whine noise goes up with throttle). At highway speeds it will cut in and out sometimes (weird). The sound is pretty much present at constant speeds from 45-90. It's absolutely maddening and I'm about to give in and see if the tardos at the Ford dealership can fix it. If anyone has any more ideas as to what it could be, PLEASE let me know. I've got a couple of theories:

1) Air leak at the throttle plate pivot, allowing air in through the bushing. It could be either at the TPS sensor side or the cable side. I have no idea how to check this.

2) cracked plenum. (has this ever happened to anyone?)

3) bad seal between upper and lower intake (again, anyone?)

4) cracked throttle plate. I looked but didn't see any.

Like I've said, I've had someone find the whistle while the car was blocked and parking-braked in drive (yeah I know it's bad for the transmission), and we both agreed it is coming from somoewhere around the intake.

I just concluded a 700 mile road trip and am just about to go after the whistle with a hammer. It drove me absolutely nuts.

Thanks in advance,
Scott

 

[Jason_25]

I have the same thing. I think it has something to do with the IAC. Maybe the seal between it and the upper intake, or the little black cap on top.

 

[1996XLT-68]

Jason,

(IACV) I pulled it apart and cleaned it out, popped the cap off and cleaned the little felt filters, and even tried duct-taping over the vent hole to see if that helped. It didn't. The rubbber O-ring was in perfect shape and protruded all the way around to seal the gap between the plenum and the valve.

My instinct tells me the problem is not the IACV. It's usually right. I may replace it just for grins though.

 

[CBoug76]

Ok, they made 2 different types of IAC's.
The first one was made for the 91-94 models.... and this one is Cleanable, you can take it apart and clean the insides......

The Second one was made for the older Models(95-02).
Some think this is cleanable, but its NOT! you can not clean the insides out.... You have to replace it. If I knew you better, I would bet you each $20 that if you changed it, the Sound would go away! people don't want to change it because the IAC cost like $80.... and since it is an Electronic part, most Parts stores will not allow you to return it.

I had the same kind of noise, and I tried an IAC, and now that same noise is gone!

 

[jntcsc@cs.com]

try this

My 98' Sport does the same thing normally during idle. It sounded like it was coming from the air box which lead me to believe it was an intake leak around the spacer or filter. Upon further inspection I discovered it was actually the IAC valve. Try this: Run the engine at various rpm's using the throttle body until the sound is heard. Disconnect the plug to the IAC valve and the humming sound should dissapear and the idle should drop 200-300 rpms but not stall the engine. I did this on my explorer to confirm the intake sound. Will be replacing it next week.

JT

 

[Jason_25]

Mine doesn't do it when revved in park. It only whistles under load.

 

[jntcsc@cs.com]

Try turning on the AC while it's at idle. This should be similar to being under load. Mine does it more often when the AC is on.

JT

 

[jntcsc@cs.com]

Forgot one more trick... Drive around with the IAC disconnected for a while and listen carefully. It won't hurt anything but just make the engine idle real low as you check things out.

JT

 

[fastcougar]

I have an IACV on the way from Atascadero Ford Outlet (I get all my parts from them) and plan on installing it this weekend if it gets here by friday. My car has "moosed"/"howled" for the last 3 years. It only does it when the weather is just rigtht ... more often on humid days, but always if it's above like 75 and definitely if it's humid and above 75.

I too pulled my IACV apart to see if I could diagnose what exactly is going on. Here is my best decription of what might be causing this. I have pictures at home and will attach them to my explination with an edit later tonight.

1) Air comes into the engine
2) Air hits the Throttle Body (TB) and is forced to look elsewhere to go into the engine.
3) The engine is creating vaccume because it's pistons are drawing down, creating a need to be filled with air ... it's sucking.
4) Air is "sucked" through the IACV passageway on the Upper Intake Manifold (UIM).
5) Once the air enters the IACV Chamber, is passes over the back of the plunger piston and into the second chamber where the spring assymbly is as well as the air's outlet into the UIM.

6) From here, the air enters the engine and whalla, it idles because it is getting just enough air NOT to die.

The problem exist at step #5 in my air pathway list. As the IACV wears with age/use, the plunger can no longer be pushed open as far as it did when it was new. Why? Because over time, just like with your suspension, springs loose their ... spring for lack of a better word. They become less tense so to say and they relax. Since this the only part that opens the valve, the incoming air is now hitting an opening that is probably half of that it should be. Now, my theories as to the actual cause of the "Howl":

The plunger is shaped like a mushroom cap. When power is supplied to the IACV, the plunger is pushed up by the solenoid and compresses the overhead spring and closes the passageway between the two chambers. When voltage is dropped to the unit, there is no longer any resistance on the spring and it then pushes down on the plunger opening up the passageway. Now, back to the plunger shape. I think that 1 of 2 things is happening here. They are:

1) The air that is rushing in is creating a small amount of pressure ... just enough to cause the little filter assymbly to become a whistle. In this scenario, air is exhaled and vented to atmosphere though the filter assymbly. In the process, it whistles.

OR

2) The restricted passageway is actually causing the whistle as air is drawn through it. Pucker up and whistle yourself and then while whistling, relax your lips and see what happens. The whistling stops. This is similar to what is happening here. The passage way is ajar just enough to cause the whistle, but if it where new, the passageway would be larger and doesn't wistle.

I was leaning toward #1 simple because if it starts to whistle/howl and you remove the little black cap/filter assymbly, the howling stops. However, thinking about it, that would releave the pressure being sucked through the restricted passageway and would fully support #2.

So, in conclusion, I feel that the problem exists due to wear on the overhead spring responsible for the IACV plunger to open fully. As the spring wears and looses it's ability to "spring" completely, the passageway between the two chamgers decreases in size. In my examples, I refered to whistling, when in fact it definitely more akin to a howl. Jus try to emulate a howl without closing your mouth opening ... it's impossible.

So, BUY A NEW IACV and whalla, problem solved!

Dead Link Removed

 

[Jason_25]

But mine has a new one as of last year and It still does it......

 

[1996XLT-68]

fastcougar,

I think we're talking about two totally separate issues here. Mine howls at idle on hot days too. I don't care about that. The symptoms I described at the top of this post are totally different.

Scott

 

[fastcougar]

Sorry Scott ... guess I should read the entire post before replying However, your IACV could still be the cause.

 

[psychotic]

I think i have the same problem as cougar. It started after I put on my FPIK, so I guessing the more air flow was just what my "howling" needed to act up. I'll replace my IACV and hope thats the cause, thanks!

 

[RammaR]

I have a similar whistle at around 2100 RPM under load, did replacing the IAC valve do anything for you 1996XLT-68?

Thanks...

 

[1996XLT-68]

RammaR,

I haven't replaced it yet, but I pulled the IACvalve off and totally cleaned it out a while ago. The noise got a lot quieter for a while but is back now with a vengeance. So I'll be replacing it soon, probably when I get back from London next month.

 

[1996XLT-68]

Well, I replaced the IAC valve and it DIDN'T FIX THE NOISE. ARGH.