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Whistling sound at idle

I have a 1996 Nissan Maxima that is making a whistling sound while at idle.



The alternator was recently replaced, so perhaps it is related to that.



It only happens when warm and if I increase the RPMs, either in neutral or in drive, the sound stops. While coasting to a stop, once I reach a certain RPM level the sound will return.



Sometimes just shifting to neutral will stop it temporarily, but not always.



Any ideas of what it could be? …Easiest fix? …How pressing is it to fix it immediately?



Thanks.

Vacuum leak. A small vacuum hose is probably split.

When you raise the RPMS, there is less vacuum, so the sound goes away.

Thanks! Will it hurt to drive the car like this for awhile? I may not have time to get to it before traveling for the holidays.

As long as your brake pedal is still firm, then all you will probably notice is the idle being a little rough.

With the hood open (assuming the leak isn’t in the dash), you should be able to find it. If you do, some electrical tape or friction tape should fix it up for now.