Engine Whistle?

Morning all!

93' XJ 4.0, NP231, AW4, with 125K, stock except for mustang injectors.

It may have been happening longer, but within the past week i have noticed (almost always when hot, sometimes when cold (engine temp)) that i have a very high-pitched whistle going on at idle. as soon as i give it a bit of throttle it diminishes, so i assume it's a vacuum leak. sounds like it is on the top-right of the engine, close to the firewall.

i have wiggled and jiggled about all the vacuum lines around that area (CCV breather (which is new), MAP sensor, TPS, IAC and haven't been able to quite pinpoint it.

anyone have any suggestions on a better way to pinpoint which line is leaking? I haven't tried spraying carb cleaner or removing lines and plugging them yet, but I'm kind of guessing those are my only other options, right?

As always, thanks for your input!

Check your TB and the air tube on top. It's definitely vacuum

thinking about it, i had a very low idle about a month or so ago, pulled the IAC and cleaned it carefully and reinstalled it (no gasket). fixed my idle problem, but i thought it was odd that there wasn't a gasket there. should there be?

i will pull the air tube it self and bend it around to see if i can find some cracks in it. and by TB, do you mean where it meets with the intake? or more where the sensors and air tube are connected? or all of the above lol!

when i replaced the CCV breather tube, i didn't replace the elbow in the VC, however, when i replaced the VC gasket ~1 yr ago, i cleaned it out pretty well with brake cleaner. can that be replaced without removing the VC?

thanks!

Not sure on a '93, but my '89 has vacuum going to the cruise control as well. Are all the bolts to the intake manifold tight?

No CC on my XJ. I will check the manifold bolts as well. i replaced my exhaust manifold last year and employed loctite as instructed on here, but i will definitely check those as well since i have read numerous posts on these backing out after a little while.

Don't know about yours, but my 88 has a oring at the base of the IAC near the flange for sealing. I did an exh mani swap a while back and had that confounded whistling. A few others recently did as well.

Take the air tube off the top of the TB and see if it happens. You can also look down the opening for the IAC and double check to make sure it's clean.

it seems like it would have a oring or gasket of sorts to help seal it, im not finding a listed part on advance auto website, but that doesn't mean it doesn't exist

i will add the air tube to my list of checks i have going. thanks!

hightime81,

This technique may, or may not, be useful to you but it worked for me pinpointing a whistling type noise in my engine bay.

Get a 3' piece of 3/8 ID vacuum hose, or similar soft hose, and nest one end in your ear and move the other end around to suspected noise sources, even in the openings on the intake manifold next to the cylinder head. The hose has a tendency to focus sound when held close to its source, where the human ears will gather all sounds and make it difficult to pinpoint a sound source even when close its source.

Needless to say, be careful around moving belts and such.

Follow SidewinderCC's advice.

One spot many overlook is the throttle plate shaft where it passes through the throttle body--gets worn and you end up with a leak there. Smear a little grease down in there and see if it quiets down if that is the area you isolate it at.

I had the same problem . after much searching I found a very small crack in the 90* plastic fitting that goes into the vacum booster. no mo noise and better idle. Hope this helps.

I had a very similar problem on my 01 TJ....intake manifold bolts had come loose creating a very small leak at the intake....check your intake/manifold bolts...I'd bet that is the issue.

I had all the intake bolts slightly loose, just need a 1/8th turn or less to snug them up again and the whistle went away.

so i went at it with a hose and didn't isolate the whistle to any of the 'normal' offenders on the top of the intake and CCV.

so i am definitely leaning towards the manifold bolts being loose. i will have to check that tonight/tomorrow.

on what i believe is unrelated (but still could be lol), i noticed that my VC is starting to weep a bit (replaced early this year), so i either have two issues at once (crankcase being pressurizecd and i need to replace CCV elbow) along with the loose manifold bolts, or that pressurization is causing a whistle at the CCV elbow that i can't quite isolate.

is it easy to change that elbow for the CCV, or do i have to pull the VC?

So a quick update:

pulled the airbox, CCV breather tubes front and back, pulled the CCV elbows out of the VC (front and back).

cleaned it all up. the rear elbow from the VC was pretty nasty too. no cracks found on any of the vacuum hoses.

cleaned the throttle body some and made sure the rest of the vacuum connections on the intake were in good shape and they were.

went on to checking the intake/exhaust manifold bolts. not much to mention until near the back where one of the bottom bolts took a good 2-3 turns to tighten back up. slapped everything back together and started the engine.

oddly enough, saw just a tiny bit of smoke, and smelled like something was burning but it was gone quickly (assuming the carb cleaner burning off)

whistle seemed gone, but then came back, only much softer. i started pulling vacuum connections to see if i could pinpoint it and the only time i really noticed it go away was when i pulled the vacuum that goes to the MAP sensor. but when i did that it almost cut off from the low idle, so that could be unrelated.

took it for a drive and didn't really notice the whistle, stopped and couldn't hear it at all. then on my drive home, i noticed it again, but VERY soft again. So it is definitely intermittent which makes me think it is not related to manifold fit (not anymore at least).

even though i cleaned it pretty well, i think i might need to replace at least the rear plastic VC elbow. i think it is causing the vacuum somehow with the breather hoses. carb cleaner sprayed carefully around the sound didn't have an effect on idle. Could the MAP sensor cause the whistle somehow?

as long as i have owned it (6 yrs, ~80K) i have never changed the VC elbows... nor the MAP (or any sensor other than the oil pressure sender).

any opinions? anyone live near Raleigh want to come listen to it LOL!

have a great weekend!