So, I'm still trying to figure out where that whistling sound is coming from when I'm accelerating. I'm crawling around the engine compartment shining a flashlight on everything I can think of when while rooting around the intake manifold I find this little piece lying loose. It looks like the stopper at the end of the check valve that comes off the smallvac tube on the mainfold, but that one is there (and this mystery part is larger.) anybody got any ideas what it is?



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Looks like a vacuum line cap.

 

That is def a vac line cap, and if you are missing one somewhere then thats probably where the whistling is from. I know mine has a cap on a nipple on the side of the intake manifold in addition to one thats on a check valve. Just keep shining with the flashlight and I would think you would find where it went. I've also heard of people using a length of rubber hose or pipe and holding it to the ear and fiddleing around the intake to try and isolate hissing sounds, you could try that.

 

Vacuum cap for sure. Has anyone else done any work on your truck. If so, maybe they misplaced/dropped it and put a replacement on. Just a guess.
Can you hear the whistle while you're under there? Or, only when driving?

 

Actually, I'm the one that did it, when I replaced the plenum gasket last weekend.That is when the whistling started, so I'm pretty sure I knocked it off, just don't know where from.
I only hear it when I'm driving and accelerating around 1700-2000RPM. I've tried having someone rev it inparkto thoseRPMs and listening under the hood, but the damn thing won't whistle unless I'm moving.

I figured it went to a vac line as it looks just like the one on that large run ofvac lines on the passenger side of the intake, just can'tfind the spot it goes on.

Maybe I should change the name of the thread to, "Where the heck does this go?"

 

HAHA, I tried to leave you an OUT, but since YOU went there...
Let me go out and have a looksee at my '01 and see if I can locate it.

 

Thought I just sent this, but don't know if it went through.
I think this is what you say you have. It's all I can find with a cap.

 

Yeah, I have that one, just PMed you a possibility though.

The spot I think it is looks like a bolt might go in there, but would also explain why the part fell out so easily when I lost vacuum working on the truck. You'll probably need a flashlight to see it. It'll be standing up like in the third picture if I'm right. Probably used to stop off a vac line from the intake so they wouldn't have to redesign for the 2001 TB that doesn't have a vac line in the back, or possibly for the older EGR unit, though I don't know what that looks like as I don't have one.

 

I think that those are what I was looking at. Possibly a mount for some option or control that we don't have. Mine do NOT have any caps/plugs in them. I just mailed you info out of the on-line manual, but don't know if the illustration shows a cap or just a one dimensional view of an ell to the MAP sensor.

 

While letting the truck run, after warming it up, take a spray bottle of water and start heavily misting/spraying sections of the top of the engine. If you get a sudden bog or high idle, that will at least let you know the area you need to be looking in. I've used carb cleaner from a can in the past, but you always stand the risk of having a quick flash of flame if it combusts while spraying. But the advantage to using that is you get a very sudden high idle when you find the vacuum leak.