Reverb2005

So I have been trying to track down a leak somewhere in either my exhaust or intake and I would like to know where the heck these two nipple fittings go that are attached to the intake manifold.

K, see just below where the throttle body sits? One goes to "E-1" and the other goes to "B-24/B-24-1". I know it is NOT the PCV port, that is along the side of the intake, oddly enough where the image shows a "cap" goes (#20). My guess is that one of the ports is for the EVAP system, but the other??

Since I'm posting this, I may as well ask about the leak I am looking for. My car runs perfectly fine, no problems, no CEL, good mileage, passes e-test, etc. I have heard this noise for some time now and just never did anything about since it doesn't actually seems to negatively affect anything. The noise is a "fluttering" noise, like a very quickly fluttering piece of sheet metal or something. It only happens when I let my foot off the throttle and I am decelerating. Any slightest tap on the throttle and it is gone! It is NOT a bearring and it is definitely NOT the input shaft bearring as I have already had that go and replaced. I have heard others say it could be the EGR valve making noise and I am going to take that off this weekend and clean it and install it with a new gasket, so maybe? It's just annoying and I want to figure it out, lol.

Also seems doubtful that it is an exhaust leak. I have scoured the exhaust manifold and downpipe for leaks and cannot find anything. The annoying thing is, is that I can't use a stethoscope in the driveway because it will only make the noise under high vacuum conditions, that is, when the car is decelerating under load....

ezone

One for the EVAP line, other nipple is ...... for the brake booster. B-24-1 is the panel with the brake booster in the parts catalog.

I don't suppose you have video of it?

Cracked plastic manifold?

Reverb2005

Ahhh, yes, the other line IS for the brake booster. Can't believe I missed that, the line goes right into it... thanks.

I did try to make a video but it is really difficult to hear in the vid. It is pretty hard to distinguish between it and engine noise.

When you say "cracked plastic manifold", to which are you referring to?

Funny thing I noticed when taking off the resonator box to get to the EGR valve a bit easier, I noticed there is no hose clamp of any sort affixing it to the air cleaner box. Is this normal? Is it just a snug fit?

Redneck_cdn

Just re-read you last post, just a snug fit on the coupling between the filter assembly and the intake resonator on mine,

if you are removing the entire intake/filter housing from the top of the throttle body there is a metal band clamp that should be present to help seal/secure the housing. #10

ezone

The plastic intake manifold. Someone posted they had one cracked after doing a head gasket or something, I was guessing maybe it got dropped on the ground or maybe they tried to pry it up before they found the fasteners on the bottom.

Reverb2005

You mean the air cleaner box? The thing that holds the air filter? Isn't the actual "Intake Manifold" metal?

I'm trying to think of this logically...... when the engine is choked, that is, when air is not allowed through the throttle, where else is it being pulled from? Or better question, where is the vacuum the highest?

1) Around the edge of the butterfly valve in the throttle
2) Intake manifold gaskets (cracked/leaking?)
3) Fuel injector base gasket
4) Throttle body gasket

Has anyone ever had/seen a cracked intake manifold or throttle body gasket? How the heck could that ever crack? I can imagine an exhaust manifold gasket cracking from heat maybe, but the intake?

ezone

Intake manifold item #9 in your parts diagram.
No, it's black plastic.
Or maybe some type of nylon or something, I'm not trained in plastic identification. Definitely not metal on a D17.
The only place it SHOULD be pulling air in freely is through the IAC port inside the throttle body.
There will be a miniscule amount of air going around the throttle plate, that's normal.

Any other air entry points would be vacuum leaks. (except for the PCV system and breather tube in the valve cover)

Gaskets like #1 and #10 are silicone rubber and have never been a problem for me.

Your fluttering noise.....
Gasket #8 might make a buzz if the manifold hardware wasn't tight, like a reed vibrates in a wind instrument?

Make sure the noise isn't originating in the exhaust, either under the car or the cat heat shields

Use a length of hose stuck to your ear as a stethoscope and probe for the noise while someone else sits in the drivers seat and causes it to act up?

Reverb2005

Of course, you're right, lol. I have never had to do anything with the intake side of things, so I have just never seen it up close and personal.

I suppose it could be a crack and I totally forgot about the IAC valve.

With the IAC valve, would you expect the valve to be open or closed when decelerating in gear, with the RPMs between 2500 and 3000?

I assume the way the IAC works is, the ECU reads your RPMs and opens the valve accordingly as well as injecting the appropriate amount of fuel. However, when decelerating, in gear, at higher RPMs, there is already power going to the engine from momentum so "should" the IAC valve be closed in this case? Just want to make sure I've got that right.....

I am going to check those manifold bolts and make sure they are tight. The sound is definitely metallic, I think anyway, so that gasket could be a source.

ezone

I'd expect closed, or at least mostly closed.

I know it isn't held wide open under that condition, if it were you wouldn't get any engine braking at all.
A wide open IAC might allow enough air to get the engine going 3000 rpm or higher.


The computer has various 'target' rpms programmed for almost any set of conditions (the engineers thought) it could ever possibly encounter, and it controls the IAC valve opening to obtain enough air flow to meet whatever idle rpm need as it sees fit.

Fuel delivery is calculated elsewhere based on running conditions, not by the iac actions directly. IAC only controls airflow bypassing the throttle plate.

HTH