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The symptom: while accelerating, at a very particular throttle level/pedal angle my engine recently started whistling in a very high pitch. If I let go of the gas or push it in more the sound goes away.

I said that this is new. To be more exact this started happening after I was diagnosing something else and did two thing:

  1. I lowered the idle, which was too high
  2. I checked for vacuum leaks using carb cleaner all over the intake system while listening for any change in the idle. Nothing was found.

Is it possible that I have an air leak that I haven't found? If so, is there a (better) method of checking for vacuum leaks that will allow me to find a more subtle leak, that might not show itself when using the carb cleaner method?

Also, is it possible that the whistle is absolutely benign and I'm worrying about it too much? I cannot seem to replicate it while the car is standing still, it seems to either need load on the engine or moving air.

I am driving a 4 cyl 1993 Acura Integra, no turbo. About a year ago I replaced the stock intake with a cold air intake (the noise is new, however).

Update: I tried to check the PCV valve and it crumbled in my hand. In the process of replacing it. Hopefully that's what it was.

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Please provide more information about your specific vehicle. For example, are you driving a turbo car? –  Bob Cross Oct 30 '13 at 1:18
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Is this the original intake or something custom? –  Bob Cross Oct 30 '13 at 14:29
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@EvanParsons aha. my elbow is made of metal but I'll give the rubber sleeve that connects it to the throttle body another look over, just in case. –  vlsd Oct 30 '13 at 17:09
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Can you get the car to make the whistle sound when parked and revving? You could probably eliminate the entire CAI as a potential source of problems by putting the factory air box back on and then check to see if the sound went away –  Evan Parsons Nov 4 '13 at 12:41
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Check online for people who have your specific CAI to see if they have the same issue. Most stock intakes have a silencer on them to squelch whistling type noises. I'd bet the aftermarket CAI not having it is your issue here. Considering the testing you've done, I doubt you have a vacuum leak. As an aside, you can use water in a mister instead of carb cleaner to check for vacuum leaks. When you find a leak, you will hear a drop in idle (idle fluctuation) as the hole is plugged. I believe carb cleaner is flammable, so could cause a fire. –  Paulster2 Dec 13 '13 at 18:49
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1 Answer

HAHA! I had this EXACT problem happen on one of my motorbikes. Basically the velocity of the wind hits a perfect speed over either a crack in the intake pipe, or some other object, and it whistles.

I'm not really sure why you would bother with cold air intakes. At best they only really provide the same level of gains as a better air filter. There are people that disagree, but I don't see a reason to even bother. I've removed them from cars and seen better gains.

Now, back to your question.

On my Odyssey (ATV with a big intake in the back), there was a crack in the plastic on the intake. Repairing the crack fixed the problem. If replacing the pipe doesn't fix the problem, you should check anything along your intake, it is most likely something that the intake air is screeching over.

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