2001 XJ Random Vacuum Leak Issue with Smoke Test Result...Need Advice

[JMA_2001XJ]

So on my 2001 XJ I have an random vacuum leak when I come off throttle. It is a high pitched whine only on deceleration with no throttle input. But it only happens sometimes and seems to be totally random. I can usually drive about 5 miles or so on a cold start before it will begin and then it will continue for the duration of my drive or sometimes it will just stop doing it after awhile. It does not do it at idle. Occasionally when I come to a complete stop it will continue for a little while. It will continue long enough that I traced it to the engine bay. I initially thought that it was coming from behind the dash and had to do with the HVAC system (the common vacuum leak area). But one day when it was doing it and I came to a stop and it continued, I opened my window and it got louder, I quickly popped the hood and it got much louder, and then abruptly stopped. I can't duplicate it without driving the Jeep.
My buddy has a smoke machine so I tried it out. The only place that smoke was coming out was the throttle body butterfly shaft, nowhere else and I let the machine run for 20+ minutes. I have read that the bushings can go bad, there did not seem to be much play in the shaft, but there was a pretty good amount of smoke coming out.
Before I go and buy a new throttle body, I was hoping that there was someone else that may have had this issue and can chime in. Thanks in advance.

 

[lawsoncl]

If you think it's throttle body shaft:
https://www.youtube.com/watch?v=ASvpGGE-XHU

 

[cruiser54]

Snug up your intake manifold bolts.

 

[Saudade]

Have you done any other work recently on it?

Definitely sounds like a vacuum leak. When mine did it, it was an intake manifold leak. However, I had just replaced a cracked exhaust manifold so I knew where to look.

Once the engine is warmed up and "whistling", you can open the hood, grab the throttle linkage and quickly rev the engine to 3000-3500 rpm (or close enough) and then abruptly, let the throttle go. The should create a very high vacuum and whistle until the vacuum drops. Perhaps this will help pinpoint it.

Good advice above. Also tighten your TB.

 

[JMA_2001XJ]

I have done some work on the XJ but the vacuum leak pre-dates that work. And it was on the cooling system and suspension.

Thanks for the good advice and the link. I will definitely try tightening the intake manifold bolts and also the throttle body trick. Although I doubt it is the intake manifold as there was no smoke coming out in that area, just at the throttle body. Is there a gasket between the throttle body and the intake manifold that I need to replace when I take the TB off?

 

[90xj06]

are you getting any check engine lights? i wonder if its related to the evap system. I'm not sure where the solenoids are located on that year but if it goes to do a vacuum check and opens the solenoid and there is a leak after it could be your whistle.