High Pitched Whine / Whistle at Low Throttle

[c_woodruff91]

Hi there,

I've got a 2001 TJ Sport, 5-speed manual. I notice a high-pitched whine / whistle-like noise that comes and goes inconsistently, but appears to be associated with these common factors:

1. In gear, but low-to-no throttle (noise comes and goes consistently with relaxing and intensifying of throttle)
2. After the engine has started to warm up (i.e., it doesn't happen as soon as I start driving, but when the coolant is at, say, 140 deg or more)

The noise is present regardless of whether the radio is on or off, or whether the vent fan is on or off.

I first noticed it after a ~10 mile highway drive where I found myself coasting toward some traffic in 5th. However, most recently, I could only reproduce it at backroad speeds in 2nd or 3rd - once I got on the highway and into 5th, it went away. I would say that maybe this had to do with the engine being was fully warm at that point, but it would have been fully warm in the first case (traffic on the highway) too.

I'll try to reproduce it more consistently, and get a recording. It also seems there are some similarly-titled threads on here already that I'll check out. But I figured I'd post early in case anyone more knowledgable than I has an idea.

Thanks!

 

[03coloradowrangler]

exact same on mine although i have convinced myself its just a jeep thing because it doesnt sound like anything really concerning and is always there at very low throttle

im also stumped

 

[c_woodruff91]

That would certainly be a cheap solution!

I'm in the same boat, nothing *concerning* about this necessarily. Just hope it's not an omen of something else. And so I'm being an oversensitive Jeep owner.

 

[Jodh]

Does it sound like a vacuum leak? Mine had a whistle sound when it was cold turned out the intake manifold was somehow loose. Re-torqued it back down and it went away.

 

[c_woodruff91]

I'm not sure how to identify that by sound. But, I haven't noticed any obvious weirdness with the idle RPM. I'll double check the idle RPM tomorrow, with the engine cold and warm, just to be sure.

 

[Camdenst]

Try cleaning out the throttle body, specially the idle bypass. I had a pronounced whistle on idle and driving around town when not on the throttle.

 

[Mjv]

Whistle is a definitive air leak. Could be vacuum or positive air flow. Smoke test is warranted. Have seen them done. They work.

 

[creecer]

I'm not sure how to identify that by sound. But, I haven't noticed any obvious weirdness with the idle RPM. I'll double check the idle RPM tomorrow, with the engine cold and warm, just to be sure.

Do you have an OBD reader, or Torque? You should be able to monitor engine vacuum from the PCM. It will give you an idea about a vacuum leak.

 

[c_woodruff91]

Thanks for all the suggestions. I've been super busy, but should finally have some time next weekend to take a closer look.

I don't have an OBD reader but could easily get one. You're saying I should be able to monitor vacuum stats even if there aren't any errors firing?

Also, as an aside, could a vacuum leak hurt gas mileage? MPG is a bit lower than I'd expect, and the logic in my head is more air intake is compensated for with more fuel. But I'm not sure if that's accurate.

 

[creecer]

Yes, you can get a good idea of a vacuum leak by using a gauge/reader. Here is my Torque layout. I use an Android double din head unit and a bluetooth ODB2 connector. Vacuum is in the middle, under the speedo.

 

[reddvltj]

My first thought would be a vacuum leak of some kind. Specifically because you stated that it only happens at idle and while off the throttle when driving. That is when your engine produces the most vacuum. You can use carb cleaner or propane to narrow down where a leak is. There are plenty of videos showing how to do this.

 

[Cooz]

Same problem with mine. I tightened all the throttle body screws a full turn and noise went away

 

[c_woodruff91]

I tightened down the throttle body - the bolts moved easier than expected, and I got about a full turn out of each, maybe more. Took it out for a spin, and the whistling is still there.

I made this video example:

(Just ignore the fact that I'm recording while driving, with no seat belt. It's a long quiet road. )

I'm not as confident in the vacuum leak theory, because the idle isn't high and check engine isn't on. Also, I found this article which implies that vacuum leaks are noisiest when the engine is cool. Mine is the opposite - doesn't appear until the engine is warm.

Lastly, after I stopped recording, I drove another mile or so to my driveway, and the noise at stopped completely (no noise while coasting, no noise while idling in the driveway). So, it's unpredictable, to a certain extent.

 

[Cooz]

I tightened down the throttle body - the bolts moved easier than expected, and I got about a full turn out of each, maybe more. Took it out for a spin, and the whistling is still there.

I made this video example:

(Just ignore the fact that I'm recording while driving, with no seat belt. It's a long quiet road. )

I'm not as confident in the vacuum leak theory, because the idle isn't high and check engine isn't on. Also, I found this article which implies that vacuum leaks are noisiest when the engine is cool. Mine is the opposite - doesn't appear until the engine is warm.

Lastly, after I stopped recording, I drove another mile or so to my driveway, and the noise at stopped completely (no noise while coasting, no noise while idling in the driveway). So, it's unpredictable, to a certain extent.

That’s exactly what mine sounded like. I also was able to tighten an intake manifold bolt near the firewall.

 

[B00mb00m]

I tightened down the throttle body - the bolts moved easier than expected, and I got about a full turn out of each, maybe more. Took it out for a spin, and the whistling is still there.

I made this video example:

(Just ignore the fact that I'm recording while driving, with no seat belt. It's a long quiet road. )

I'm not as confident in the vacuum leak theory, because the idle isn't high and check engine isn't on. Also, I found this article which implies that vacuum leaks are noisiest when the engine is cool. Mine is the opposite - doesn't appear until the engine is warm.

Lastly, after I stopped recording, I drove another mile or so to my driveway, and the noise at stopped completely (no noise while coasting, no noise while idling in the driveway). So, it's unpredictable, to a certain extent.

Hey did you ever find the source of the ringing / whining / whistle? This just showed up for me. The whistle does not appear to be rpm related. The whistle goes away when I slow below 10mph. It's some what intermittent. It does not change pitch or volume with speed.

I have recently had random rough idle at startup every now and again where it's like stumbling idel then give it some gas and it runs fine never another hiccup.

I made a video:

 

[barrios35]

That’s exactly what mine sounded like. I also was able to tighten an intake manifold bolt near the firewall.

Just had the whine come up thought it was a dirty throttle body. Took it apart and cleaned it all up. It came back. Tighten down the intake manifold bolts and it seems to have fixed the issue. Some where real loose especially by the firewall! I was shocked. Thought those where so hard to come off.

Thank you all for the solution!

Video in case this may help someone down the road .





Anyone know the torque on them by any chance? I would hate to break one.

 

[B00mb00m]

Ya that is for sure a vacuum leak whistle. For the record, my whistle ended up being transfer case output nut and/or seal.

 

[Abbott]

I tightened down the throttle body - the bolts moved easier than expected, and I got about a full turn out of each, maybe more. Took it out for a spin, and the whistling is still there.

I made this video example:

(Just ignore the fact that I'm recording while driving, with no seat belt. It's a long quiet road. )

I'm not as confident in the vacuum leak theory, because the idle isn't high and check engine isn't on. Also, I found this article which implies that vacuum leaks are noisiest when the engine is cool. Mine is the opposite - doesn't appear until the engine is warm.

Lastly, after I stopped recording, I drove another mile or so to my driveway, and the noise at stopped completely (no noise while coasting, no noise while idling in the driveway). So, it's unpredictable, to a certain extent.

You are not crazy I have this exact issue with my 2004 4.0 wrangler. Warms up then starts to make noise at what I would say are High Vacuum times. Just after a shift or when I'm slowing down in gear. Touch the throttle and it goes away. Play with the throttle and you can get it to change pitch. Did you figure out a solution?

 

[barrios35]

You are not crazy I have this exact issue with my 2004 4.0 wrangler. Warms up then starts to make noise at what I would say are High Vacuum times. Just after a shift or when I'm slowing down in gear. Touch the throttle and it goes away. Play with the throttle and you can get it to change pitch. Did you figure out a solution?

Yes, for me it was the manifold leak. Tighten the intake bolts and check the header bolts while you are at. I think they were 25lbs torqued but can't recall.

 

[StarterKit]

I tightened down the throttle body - the bolts moved easier than expected, and I got about a full turn out of each, maybe more. Took it out for a spin, and the whistling is still there.

I made this video example:

(Just ignore the fact that I'm recording while driving, with no seat belt. It's a long quiet road. )

I'm not as confident in the vacuum leak theory, because the idle isn't high and check engine isn't on. Also, I found this article which implies that vacuum leaks are noisiest when the engine is cool. Mine is the opposite - doesn't appear until the engine is warm.

Lastly, after I stopped recording, I drove another mile or so to my driveway, and the noise at stopped completely (no noise while coasting, no noise while idling in the driveway). So, it's unpredictable, to a certain extent.

I have this exact sound but in total opposite way. It happens when I try to accelerate under same conditions ie. driving for a while, engine warmed up, typically after 35-40mph and when I press the gas pedal down more, it goes away. So I sort of coast drive the Jeep, where I lightly push the pedal to gas, when the sound comes on, i let go, press gas pedal again, gain more speed, and drive it that way. What could it be?