Random XJ Whistling Noise

Hello all,

This is my first post and hopefully not my last! I am very glad to find such a knowledgable group of people that have the same vehicle interests that I do!

I have a 01 XJ with about 70K miles on it. Just recently I noticed a "whistling" noise coming from what sounds like inside under the dashboard, on the drivers side. Here is the interesting part: this only happens while coasting (no throttle at all) at speeds above above 35MPH and it will go away if you wiggle or tap the accelerator gently with your foot. It will also do this if you use the cruise control, no "whistling" while the cruise is set but once you use the coast feature or shut it off, the whistling comes back. It will even "whistle" while braking down to about 35MPH, then I'm not sure if it just stops or if it is just so quite that I can't hear it anymore. The speed of the vehicle doesn't seem to affect the volume or pitch of the "whistle." Also, this doesn't happen everytime I drive it, I can drive 30 miles at variuos speed and it will never whistle, then I can run down the street to the store and then it will "whistle" while coasting to a stop sign.

I really appriciate any help that anyone can provide me, this is driving me nuts and I would like to know if other people have had this problem too!

I'd check all the connections from your air filter to your throttle body. Mine whistle sometimes when I shake them loose on the trail.

Aside from that, let me beat everyone to saying "vacuum lines" Dive in head-first and chase ever little black hose where ever it goes. It's an adventure.

Thank you very much for the info. I will have to try that when I get home from work. I was tinkering with it earlier today and thought I had it with the CCV assembly coming out of the valve cover, but much to my disappointment, after cleaning it up and I got it back on the road to test it and it still whistled. I did actually get it to duplicate the problem parked and I think I narrowed it down to the firewall side inside of the engine compartment. I have problems getting it to keep making the whistling noise while parked so this should be fun!

I had a similar problem, it was the tb gasket, replaced it and everything was fine.

Basically it is whistling when in high vaccuum situations. You have a leak somewhere but it whistles when the vacuum is strongest. What happens when you manually downshift coasting and let off on the gas? This would be high vac. because the throttle plate closes while engine speed is held high. Here are some starters:
1.) the brake booster (line or internal, look at the shaft where it connects with the brake pedal)
2.) the heater controls (and the door thing that opens/closes with AC, the heater valve)
3.) cruise control components?
4.) Other vaccuum leaks you might not be inside but you hear them, MAP sensor? Evap. cansiter. Throttle body area or manifold gasket at head.

Trace the lines coming from the manifold.

Is the throttle body gasket an easy one to replace? I can't imagine it would too expensive. Thanks for the information, it will help my ongoing trouble shooting later today!

Bajacalal - I checked the external line going to the brake booster, it appered ok but I didn't check the shaft going into the brake pedal. As far as the heater controls go, they all seem to be functioning fine and it still makes the whistle no matter what position it is in, that said, could it still be leaking from that vaccuum door control thingy? Is there a way to test the MAP sensor or Evap canister specifically for leaks other than visually inspecting them for cracks, ect? I really do appriciate all the help that everyone has given me so far!

You can try to spray some grease or something on things. You can disconnect and plug (w/ nail) the lines at the manifold and try to repeat the situation where it whistles. If it stops then you found the leaky item. Cracks in rubber grommets are almost guaranteed leak. This won't work for gaskets though. Some mechanics introduce propane from an unlit torch -be careful- to different areas to see if the engine richens up (where the propane leaks in). Can be hard to check richness w/o right stuff though. Try to listen closely. It is common for boosters to fail and do things like this (esp if it starts eating its own brake fluid after when the master cyl. seals fail). Does pushing the brake pedal affect anything?

I haven't tryed anything with the brake pedal when it was making the whistling noise, but I will tap the brakes next time it starts it up..... Thanks again!

about ten minutes and i just used cork sheeting, pull the tb, trace, trim, cut, add tb, torque to spec, DO NOT OVERTIGHTEN, unless you like shitty creek with no TP.

Thanks acrid! Sounds easy enough, I will let you how it turns out!

i hope that's it.... otherwise, it's a real pain to find vacuum problems.... good luck

king282 said:

Thank you very much for the info. I will have to try that when I get home from work. I was tinkering with it earlier today and thought I had it with the CCV assembly coming out of the valve cover, but much to my disappointment, after cleaning it up and I got it back on the road to test it and it still whistled. I did actually get it to duplicate the problem parked and I think I narrowed it down to the firewall side inside of the engine compartment. I have problems getting it to keep making the whistling noise while parked so this should be fun!

Click to expand...

My wifes 99 WJ does the same exact thing! I happens about 1800 rpm, mostly in town. I've been trying to figure it out, but no luck. I would be interested in seeing what you find.

Mike Harris

I had the same deal thought it was the vac mtors onder the dash... not them... turned out to be a leaky TB gasket

yeah, mine progressively got worse until it was a full pitched whine at idle, took about 2 months to go from occasional whistle, the only problem i had, is that when i tried to trace it, it would disappear. lol. at first I thought it was the tb spacer and open air intake just getting whiney.

Vacuum leaks are easy.
Use starting fluid and spray until the engine idle revs a little.
That's your leak.

tireroastin93XJ said:

My wifes 99 WJ does the same exact thing! I happens about 1800 rpm, mostly in town. I've been trying to figure it out, but no luck. I would be interested in seeing what you find.

Mike Harris

Click to expand...

rev the throttle to the problematic rpm while you're under the hood, see if that helps to trace it.....

acrid said:

rev the throttle to the problematic rpm while you're under the hood, see if that helps to trace it.....

Click to expand...

Thanks, I'll try it out and see if it does it.

Mike

Well, once again I would like to thank everbody that has been posting suggestions to help me fix this very annoying problem. I replaced the throttle body gasket, checked every single vaccuum line (even replaced 1 or 2 that were craked), checked the brake booster, and checked all under dash HVAC controls. It is still whislting. I have managed to do a little better job diagnosing it, for what I describe as a whistle seems more like a pulsing whistle type noise, if that makes sence. I can duplicate it at a slower speeds as long as the engine is at a higher RPM. I have also been able to duplicate it while parked, but only for short periods of time, I can give it a burst of throttle, and as it comes back down to an idle it will whistle. However, while parked and after revving it 5 times or so, the whistle will just stop and not come back till you drive it again. The noise is coming from the drivers, firewall side of the engine compartment. I was curious if it could possibly be a fuel issue (I think that is my next plan of attack) or if I am just missing something huge. I feel stupid putting this much time into an "annoyance" but it is a personal quest now! I appriciate any help that anyone can shed on this issue. Thanks again, Bill

By your description, you have located the general source. I have to throw this in though. I couple of months ago, I had a whistle coming from under somewhere. I could not locate it since it only happend while driving! Only between 25 and 45 MPH and intermittantly (sp?).

It was the bearings in the alternator. I ignored the whistleing and then noticed a bigger noise problem. Thought it was the Idler bearings. Replaced it without change. Thought it was a spun bearing on the crank. Nope. Alternator. Ain't it fun!