Help: Whistling / Squealing noise at about half throttle!
 

Hello All,

My 94 Ranger 2.3L with 5-speed manual just started making a whistling / squealing noise at about half throttle that behaves like a vacuum-related issue. It gets a little quieter as I pass through on acceleration and if I back out of it when I hear the noise it gets a little louder and squealier as it comes down. I can hold it at that level on slight hills but I can't repeat it in the shop because half thottle revs up pretty fast without load. If I let off too much or press further down on the throttle it goes away. It's almost the same sound and volume as a small flock of birds outside the window. I don't think it's belt related since it seems independent of engine RPMs. I've read in other threads that it could be an IAC valve going bad but it idles and accelerates smoothly so I'm not sure. Also, my truck failed the idle emissions only (great cruise emissions) so maybe it is the IAC and it's all related? Any input here would be appreciated.

Thanks!

Are you sure it's coming from the engine? I know it's kinda hard to check, but have someone drive the truck and hang your head out the window. It sounds to me like maybe a transmission or torque converter/clutch issue.

It's hard to diagnose a sound with just an explanation of it, but here are some possible issues:

• Wheel bearing failure or pre-failure
• Brake pad friction or wear-indicator noise
• Minor vacuum leak
• wind noise

Out of all the options, I would suspect it's a minor vacuum leak. Normally a vacuum leak has other symptoms, like rough running conditions. However, if it's a small opening on the intake manifold, it would cause a noticeable whistling noise.

Good luck trying to pinpoint the area the noise is coming from!

Thanks for the reply. I would put my money on the minor vacuum leak but I can't seem to figure out where it's coming from. Since the sound is throttle position dependent and not wheel speed dependent I think the other items listed are probably not the cause. I have a hunch that it's probably a simple fix but I'm not sure where to start since I can't hold it at half throttle long enough to find the noise in the shop. Does the idle air control valve open at non-idle conditions? If so, this could be it.

I believe it doesn't operate until the Throttle Position Sensor detects a closed throttle valve.

Since it is throttle dependent, it is indeed the engine and probably somewhere on the intake manifold.

Do you know how to hold the throttle body open by hand under the hood? Just curious....as this would be a good way to revv the motor while searching for the cause.

Yes, I tried holding the throttle open but it revs up so quickly it's hard to hear the problem without some kind of load on the engine to slow it down. I I think I would over-rev it if I held it open longer than a second or two. What a pain! I will look over the manifold again and see if there are any hoses or connectors that appear worn. It probably wouldn't take much of a hole to whistle.

The IAC is partially open during part throttle conditions under load. Then, during closed throttle deceleration, its duty cycle is reduced at a calibrated rate. This softens the sudden vacuum increase that can cause hydrocarbon spikes during decel on the emission test.

So, the IAC has 4 functions:

100% duty cycle while starting;
Feedback RPM control at closed throttle/idle speed;
RPM/load dependent "pre-position" at part throttle;
Decayed bleed during closed throttle deceleration.

Nice info! I had no basis but my own assumptions.

Based on this information, I would certainly pull the IAC off and check it's valve for functionality, then clean it with a good shot of carb cleaner or electronic parts cleaner. Blow dry with compressed air or let it drip-dry, check the gasket, and re-install.

If the problem persists, and you've checked all the vacuum connections, IAC replacement may be in order.

Let me know if you'd like any pictures of particular parts.

Thanks so much for your help. I'll start with that and report back to let you know the results.

I replaced the IAC yesterday with a new one but the noise is still there! The onld IAC was a little dirty inside so I thought for sure it was the cause.

I have the same problem, and it only happens when i'm driving at a constant speed. If i speed up or slow down it goes away, which makes it really annoying for highway driving. I think mine started after I put my intake on, but i rechecked everything and it seemed to all be tight... so i have no clue, but if you find out what it is please let me know.

its your turbo whining (:

I would enjoy that kind of whine! Now if only I can find where they hid that turbo. . .maybe it's near the muffler bearings or under that pesky spark plug arrestor cap!

The comment on the intake may be helpful. I'll take a look at mine and see if there are leaks or cracks that could cause the problem. I did recently take out my grarbox for a rebuild and I set a board across the engine to lay on while I removed the two top bolts. Maybe the boards put some pressure on the intake and created the whistle. I only noticed the sound after the gradbox rebuild but I can't be too sure since the old gear noise may have covered up the sound before the rebuild! I'll keep you posted.

Oops. "Gearbox" is the word!

I checked my intake and all the vacuum connections and everything seemed to be tight. I also replaced my timing belt idler pulley, since the original one was about to fail but still the sound came back. On cool mornings it doesn't do it right away, but begins when I accelerate from a light about a block away. I even snugged down all the hose clamps on the intake and checked the throttle body mounts, intake mounts, etc. Are there other parts beside the IAC that could cause this? Things like the PCV or EGR valves?

My Ranger will do that whistle noise you talk of every now and then at certain throttle positions. I'll go out on a limb and say it's yet "another one of those Ranger issues".

Or we can blame it on that infamous RPS curse that pisses everyone off. LMAO.

I say it's A.O.K bud. I've heard it on other Rangers too.

Maybe I'm not familiar with the RPS curse? Can you fill me in?

I read through some other posts and decided to replace my fan clutch since it is the next likely suspect. The descriptions other members have given seems to match, and it makes sense based on the type of sound I hear. If the clutch in the fan was slipping only at certain speeds that would explain the throttle position dependence to some extent. It also corresponds with not hearing it when the truck is cold because it is likely disengaged until things warm up, then it begins to engage and slip. I will report on the progress once it arrives.

That's a good likely candidate also, that most wouldn't think of right away!

Here's something to consider:
I put an intake system on my wife's Kia Spectra, and we've noticed a nice sucking/whistling noise at certain throttle positions. It could very well be a cone filter, if you have one.

mine has always had a high pitch whistle at idle, its something in the evap system i think.
or something in that general area, thats my next project for a nice day.

I have a standard stock intake setup on mine. I checked to see if anything had holes or was loose and couldn't find anyting wrong. What components are in the evap system?

it has the canister and a solenoid and flow valve attached to it drivers side behind headlight.

mine has the same 'whistling' sound.. seems to be around 2200 or 2600 rpms only. at other rpms it goes away. my iac is new.
i sure would like to find the solution to this :squint:

mine does the same thing but it seems to have multipled recently. everything is stock, 2.3L 5 speed manual. i hate tracking down noises like this....drives me nuts. the 4.0 is oh so quiet.

my K&N intake does this whistling too

my intake whistles , but this is a totally new dimension in whistling on the 2.3. its bloody annnoying