: 1997 STS Ghostly Noise from Vacuum Leak?

05-31-08, 02:34 AM
I have a 1997 STS that has been making a moaning noise that turns into a fluttering noise at random times. The noise is fairly loud and can be heard equally well inside or outside the vehicle. While driving, the noise seems to change with acceleration, getting much quieter when I let off the pedal, though still very noticable at a stop.

I traced the noise to a hose that ends up in an "L" connector (like an old spark plug cap) that fits into a black plastic nipple (for want of a better word) on something that looks like an old distributer cap located to the right rear under the plastic shield over the intake manifold. When I remove the line (while running) the noise stops completely. The line is clearly a vacuum line of some sort and there is intense vacuum at the nipple.

What I'm wondering is if there is supposed to be something between the nipple and the cap that is missing. The noise seems to be from air being pulled through the tiny gap between the nipple and the cap on the vacuum line, sometimes setting up a vibration that results in the fluttering sound.




05-31-08, 10:48 AM
Under the cover at the right rear (looking toward the firewall) vacuum operated components would be EGR (Exhaust gas Recirculation) valve, FPR (Fuel Pressure Regulator) or maybe an A.I.R. (Air Injection) valve, none of which should leak vacuum even the tiniest bit.

Can you take a digital pic, reduce the file size, and post it here??

05-31-08, 11:25 AM
Thanks for the reply. I will do that within the next day or so.

The noise is driving my wife crazy...


05-31-08, 07:37 PM
Right rear is the passengers side. That is where the EGR valve is.

05-31-08, 08:15 PM
Oh, well then left side; right if you are looking at the engine from the front of the car. The hose comes from somewhere around the firewall on the passenger side and ends up at this black plastic "nipple" on (as I said) what looks a bit like a distributor cap that is located at just about under the right rear (when looking at it from the front of the car--IOW on the driver's side) corner of the plastic shield that covers the intake manifold. I'll get a picture of it tomorrow and post it.

Thanks for the help so far!

06-01-08, 03:52 AM
Okay, camera is not going to work for now, but I think I may be able to describe it all better now that I have taken a second look at it.

What may have thrown you folks off was my description of what my memory said looked like an "old distributer cap." That visual came from some cross-wired whatever that I pulled from the 60 seconds or so I looked at the engine the other day.

This may work better: There is a vacuum line (I am pretty sure that's what it is) that looks very much like an old spark plug wire with two "L" connectors on either end that runs from the passenger side near the firewall--but connected to an assembly that is jutting toward the firewall--along and underneath the silver plastic four-bolted cover that sits atop the manifold (or what looks like a manifold) and runs all the way to the right side (driver's side) of that cover to a small bank of three nipples, each of which has an "L" shaped hose running to it and the center of which this hose is attached with the "L" connector/cap. However, the "L" connector at the near end doesn't appear to be fitting tightly to the nipple, whereas the other "L" connectors in the same location are solidly connected. Following the hose back toward the firewall to the start point, I noted that the "L" connector there appears to have a clamp that affixes it to whatever it is attached to; no such clamp is on the near end.

At best, the connection feels like a spark plug cap used to feel when the cap was over the plug, but not actually connected.

A friend actually brought me the service manual from the local Cadillac dealership, but I can't figure out what to look under to find a diagram...

I'll try again to find my digital camera tomorrow and get a picture.


06-01-08, 06:25 AM
If that's the line that is leaking vacuum and possibly causing a hissing noise at idle, do what is necessary to seal the leak. Take the beauty cover off and idle the engine, listening for leaks with a rubber tube to your ear, similar to a stethoscope.......or buy a cheap one at Walgreen or maybe a Kmart.

06-01-08, 11:15 AM
I'm about 99% sure the leak and noise is coming from the cap itself. I located the noise before I even pulled the cover off and I can see the cap moving when the noise becomes the "fluttering" type. The cap actually seems bigger/longer than the nipple. If I squeeze it when it is in place, the cap collapses to some degree. All other similar-looking caps feel solid.

This is why I mused that there may be something missing that is supposed to be in between the cap and the nipple; a valve of some sort?

06-01-08, 11:40 AM
Go to a local parts store and look in the FRAM, PartsMaster, or Delco replacement parts catalog for your year car/engine and find the oil filter/air filter/PCVvalve/gas cap/etc. parts list.

If your car has an actual PCV valve as opposed to a metered orifice, that rattle valve ($2.98) is what's missing.

06-01-08, 04:09 PM
I am pretty sure the '97 did have a PCV valve, but it is mounted in the rear cam cover on the passengers side if I remember correctly.

06-01-08, 05:51 PM
That's what I thought, and he's also talking about a tube connected to an assembly which projects toward the firewall on the passenger side.

(My '02 has the orifice type, so I'm guessing at vacuum leak possibilities)

06-01-08, 09:42 PM
Okay, photos attached.

The first photo is for orientation from the front.

The second photo is closing in on the beast to the driver's side, just on the side of the manifold. You can see the three hoses attached.

The third photo includes my fat, aging finger pointing at the center connector, the beast. You can actually see the suction pulling in the walls of the cap (the engine is running.) This is what makes me think something is missing.

The fourth photo shows the cap removed.


06-01-08, 10:14 PM
Ok, I am pretty sure that is the vacuum source for the PCV line. With the cap sucked in like that, it would make me think that there is a LOT of vacuum (plugged PCV valve). Pull the valve at the other end and shake it. It should rattle. If it does not, hold your thumb on one end and fill it with Gumout. Place you finger on the other end and shake it till it starts to rattle. Do this several times till the Gumout comes out clean, or just replace the PCV valve.

06-01-08, 11:38 PM
I think you guys have the answer. There is something on the far end of the hose that looks like a small valve between the connector and where it fits into whatever the assembly it is attached to (as you suggested, this may be the cam cover--I haven't looked at engines since cams were sitting inside the valve covers, so it didn't look familiar to me.)

How does the other cap come off the valve--just pull? I don't have any Gumout, would WD40 work?

Either way, I thank you for the help!

I'll post again when I pull the valve off and fix it to let you know how it worked.

Thanks again.


06-02-08, 12:28 AM
Whoops... That didn't work.

I pulled the hose from the far end and pulled the pcv valve, but it sounded just fine (rattled great) and even looked new (I bought the car about 1 1/2 years ago.) I sprayed it with WD40 just to make sure things were loose. I also made sure the hose was not blocked.

I put the valve and the hose back in place and there is still great suction at the near end and vibration that is creating the sounds. If I pushed the cap down on the nipple, the sound would stop, sometimes for a short time after I let it go.

Also, once the sound was gone (just for the moment,) I could hear a strong hissing sound that was clearly coming from the same location...

Since I know there is heavy vacuum (suction) at the nipple and, given your suggestion that something down the line must be blocked, seeing that there is still something stopping air flow from coming down the hose, but knowing the hose and valve are clear, this would suggest the blockage is actually PAST the valve, right??? And this would put it inside (or even past) whatever the assembly is the valve is attached to... right?

Or, is the cap on the near end supposed to have a clamp like the one on the far end and without the clamp the vacuum pulls from the nearest higher pressure source (just outside the cap)...?


06-02-08, 11:51 AM
Well, work your way back. We know that the PCV valve works and I believe you said that the line is clear. There has to be an obstruction somewhere between the cap and the PCV valve I would think unless there is something missing at the cap. My '03 engine is too difference to try to compare. My neighbor bought my '97. If no one can come up with anything, maybe I can get a peak at it some day.

06-02-08, 12:55 PM
iconokrass - Are you experiencing any other "classic" vacuum leak symptoms? Ebrake release when putting car in gear? Dash vents working properly? I'll be looking at my 96NorthStar and try and see if this is what's been plaguing me. Not sure, but it should be a similar set up as my DeVille - any one? Sounds like the connection in picture 3 is the problem child. K_C

06-02-08, 04:11 PM
Don't have access to the car at the moment. What is an "ebrake?" What should I be looking for in the vents--just that I get air from all of them when it is on?

06-02-08, 04:37 PM
Emergency brake. It releases on a shift into gear via a vacuum actuated switch - at least on my 96DeVille. your's could be electronic, not sure. Same w/ vents. W/ A/C on and the dash vents open. This too is vacuum operated. I have a vacuum leak some place. Intermittent at that. Ebrake and dash vents some times work??? Driving me crazy. As soon as I'm done stripping paint I'm pulling the beauty cover on my NorthStar and have a look-see. K_C

06-03-08, 08:46 AM
Pulled the beauty cover and see your connection. That hose comes off the intake and goes to the PVC. Connection at the intake end is secure. Your's seems to be faulty if it isn't holding the hose securely. I didn't pull mine, but it is on there tight. Guess would be there's a nipple under there the cap presses on to, might be busted. It is part of the manifold, so if the bit busted isn't on the hose end it's on the manifold end - possibly time for a new manifold. Take a close look inside that cap and see what you can see. K_C

roger greeb
06-03-08, 02:35 PM
yep pcv and dont expect to buy the fittings at advance, o rielly's nor autozone...i made my own...from tubin on the shelf..mine split on my 97 sls. cant believe u didnt experience a huge missfire...

06-03-08, 02:40 PM
Thanks Roger. I think the problem iconokrass is having is on the end were it connects to the manifold. His connection seems loose. What's under that cap the PVC hose connects to at that end? K_C

06-03-08, 05:06 PM
Try clamping it with a nylon wire tie. Cheaper and easier than a new manifold.

06-04-08, 12:16 AM
You know, I don't ever use the emergency brake, so I can't answer that question. On the vents, I'll have to check.

I did an interesting test last night... I pulled the hose again and made absolutely sure it was clear (e.g. I could blow through it with ease.) I then pulled the pcv valve and made sure I could pull air through it. And, finally, I left the pcv valve out of the equation and put the cap on the firewall end directly into the socket the pcv valve came out of and fired the engine. And I had the same problem... The cap on the near end still collapsed and made hissing and other sounds as it did in the photo when the pcv valve was in place.

I believe I understand that the point of the pcv valve and the tube running to the intake manifold is basically to vent and burn off exhaust gasses that blow past the rings into the crankcase during the combustion process by shunting them back into the combustion chamber. That means, to me, that there must be a clear line of access for the gasses that starts in the crankcase itself and runs up through the assembly at the firewall that apparently houses the cam(s) and then through the pcv valve, along the tube and into the intake manifold, making a circle of flow. I can see that by creating a port at the intake manifold (where the tube coming from the pcv valve It occurs to me, however, that if the pressure builds in the crankcase from exhaust gasses being pushed into it and that pressure (and the gasses) must be relieved

From what I have learned on this forum, this suggests to me that the blockage must actually be past the pcv valve and actually inside the engine itself.


06-04-08, 10:47 AM
If I remember correctly, you should be able to look into the 3/4" PCV "socket" in the cam cover. Shine a pencil beam flashlight in there and see if the oil splash baffle in the cam cover has collapsed and is blocking off the PCV and its vacuum source. You might be able to push the baffle back open with a Philips screwdriver.

Back 8 months or so in this forum there's a thread titled "A River Runs Through It..." or something close. It's a treatise on just that oil baffle and what can happen to it. Check it out.

06-04-08, 09:05 PM
I fixed it...

I grabbed the little bastard by his neck and wrapped a hose clamp around him. That shut him up good!

However, I noticed a split in the connector, so I assume I'll be hearing from him again soon...

Thanks for all your help. I was particularly interested in the idea of looking through the socket for the pcv valve to see if there is some kind of blockage there and when I do I'll report back.

You know, I had a mechanic look at it before and he couldn't figure out what the noise was, so I'm sure you guys saved me serious money (not that it should have cost me that much, but it would have...)

Thanks so much!

06-05-08, 09:16 AM
Hey, a fix is a fix. You saved a bundle for sure. So the cap part was at fault. Bet that hose clamp holds perfectly well. K_C

06-05-08, 11:22 AM
I grabbed the little bastard by his neck and wrapped a hose clamp around him.
:histeric: Glad you got "him" taken care of.