I know this has been asked before, but I'm trying to gain more info than what I've already read..

Since I bought my 01 XJ classic back in November it has intermittently made a loud, high-pitched whistling noise.. It only happens when I let off the gas, and goes away when I give it any gas at all. Sometimes it will continue to whistle while idling. Another thing to note is that the whistle seems to stop when my electric fan kicks on.

I've read that loose intake/exhaust manifold bolts or a bad mani gasket can cause this.. what's the best way to access these bolts to check if they're tight? Is there anything else I should check that may be causing the whistle? Thanks in advance.

 

When I replaced my manifold(s) i got the same thing. Didn't seat properly at first. The bolts came loose in a few miles. I just torqued them back down. Make sure you ONLY do this in ye proper order. Start by running your engine and spraying carb cleaner on the intake junction to the head to see if it's leaking there. Then try all other vacuum lines. Hope this helps.

 

You can listen for the spot with a short length of hose held to your ear. Another trick is to go around with short little bursts of starting fluid. If you hit a vacuum leak, the sound of the engine will change. Good luck!

That rear manifold bolt has a habit of loosening. On anything like that you NEVER want to tighten only one. It can warp/bend, even crack things. If I found that any that where easy to reach where loose, I'd pull the air cleaner and tighten them all, starting in the middle and working out towards the ends. I'd go over three times, a tad tighter each time. It's a bear of a spot to get a torque wrench on them all. Just don't ape on it. If its firm and not turning, no point in going on to break it, a REAL *****. The rearmost bolt underneath takes a little doing, but it can be done with the right extension. For that very back one by the firewall I use way long extensions (18"), with a swivel at the socket.
(Check your motor mount while the air cleaner is off)

 

Thanks for the suggestions guys.. I'll give it a go tomorrow afternoon and report back.

 

Went in yesterday and checked all the manifold bolts.. low and behold the rearmost bolt on the bottom was loose. I tightened it and now the whistle is a different pitch.. I'm thinking the gasket needs replaced

 

It is very possible that it does need to be replaced. Do yourself a favor. Get a can of starting fluid and spray it around the vacuum hoses and where you had the vac leak on the intake and make sure that it was the only vac leak that you have. When you spray the starting fluid and you hit a spot that is leaking your idle will change.

 

Yea. You'll want a new gasket of you are replacing your exhaust manifold because you didn't just tighten the bolts. (then check again with starting fluid)

 

Your jeep is just whistlin dixie. And I'm not helping you fix that gasket BRO

 

Not sure what you're saying.. as far as I know the manifold is ok?? I checked all the bolts, starting on the inner ones and working outward.

 

I'm also suspecting a manifold leak, will WD-40 or some other lube or cleaner work for this, or should I find some TB cleaner?

 

Supreme threadjacking

 

To the MAX!!!!

 

hey... the OP could've asked that question too :P

 

Lol

 

the OP's Jeep and I are familiar with one another, his manifold isn't leaky.

BTW, his jeep is a bastard, and I've shed my blood on it more than I have on mine haha