Strange whining sound from engine area

[mr_W]

hi,

I have this strange whining sound on 4.0L non-HO ('90) coming from area behind TB. It doesn't sound like mechanical sound, as it doesn't change with rpms. Sounds more like air or something coming in or out. Pitch changes slightly when i give it throttle, but quickly goes to standard.
The sound starts as soon as engine start warming up.

Anyone had similar experience ? Is this common on 4.0L ?

The sound is pretty loud, so I can hear it from inside also, but not too loud (if I turn on the radio, I can't hear this whining sound anymore).

Thanks

[LOWTECH]

Most of my Jeep whining coming comes from the passagener seat.

[98XJSport]

Sticking IAC perhaps? Or loose TB bolt...

[mr_W]

I will take off TB tomorrow for cleaning, so IAC will be cleaned also.
Hm, but as I can hear this sound even when not idling (until engine sound becomes louder). I didn't realize that IAC have function when not idling ? Maybe I'm wrong..
But will check.

Also, is there any other thing in that area that could be checked ? Some kind of leaking gasket.. maybe exhaust manifold ? Or is it on the other side ?

[98XJSport]

IAC shouldn't be working when not idling but if it doesn't close all the way due to gunk, you could get the whistling sound.

[sjx40250]

Your are lucky. My 90 has a high pitched "whine" above 25MPH. It sounds like an antenna (ususally CB) in the rain, at speed, that lost its ball tip. I don't have a CB antenna and my electric one is retracted all the way. Another way to describe it is an inverted whistle (sucking sound) at a high pitch.

I always enjoy reading about strange sounds. I have yet to see one diagnosed well. Maybe we should start a thread on : "Tell us about your strange sounds." I have one for every Jeep!

[mr_W]

I'll see whats going on in TB, and will also tighten all bolts there..
Whats usefull for cleaning out TB ? I've asked around for something to cleaning it, and all they can offer me is carb cleaner that you are supposed to put in gas tank. Hmm.. Is that stuff ok for manually cleaning it?

Also I'll take off IAC and TPS to clean them. Any hints about doing it without ruining something ?

Thanks

[rstarch345]

Vacuum leaks can also produce that type of noise. Get you can of ether or brake cleaner or whatever you prefer, and spray around those areas while the engine is running. If the engine lugs, you've found it.

[sjx40250]

Thanks for the reminder!