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Q: what vacuum activated sensors or solenoids turn on after 1.2miles or 3 minutes? on 2001 Jeep Cherokee

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after above time frame, I get avery loud whistling noise from engine area.Lines and boots are ok. Noise goes away when accelerating but return when pedal is released. I can shut engine for exactly 2 minutes and all is fine till I drive 1.2 miles or 3 minutes. This is not belt or pulley noise.
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As you accelerate intake manifold vacuum decreases (chances of hearing a vacuum leak would be less). Do you have a check engine light on indicating a lean mixture or vacuum leak? Perhaps the leak only happens as things warm up and get to operating temperature. Many automotive repair shops have a machine that generates an inert non flammable low pressure smoke that looks similar to cigar smoke. The intake manifold is sealed off, and smoke is put into the engines intake manifold. The smoke then fills the engines crankcase and if there are any vacuum leaks from gaskets, hoses, or housing smoke emits from the source of the leak. Some mechanics will use propane or aerosol carburetor cleaner, with the engine running they will spray the cleaner or propane around the intake manifold and vacuum hoses. A leak will cause a "lean mixture" condition, when the flammable fuel (carburetor cleaner or propane) comes in contact with the source of the vacuum leak the engine idle speed will raise as the engine has received "fuel". this method of finding a vacuum leak works but is not recommended as it can easily cause a fire.

Thanks Patrick, I have already shot some carb cleaner around, no effect. There are no check engine lights or codes. As an experiment,I have turned the car off whenever it starts whistling and wait 2 minutes and it goes away for the 3 minutes or so.I did this for five cycles in sucession and the noise either diminished to almost nothing or once totally gone. However after sitting for several hours it's back to square one. I'm almost ready to bite the bullet and take it to a tech,till then I guess i'll turn up the radio! Thanks again for your input. Ken

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