: INtake Manifold



akaz87
06-26-04, 12:31 AM
Hello,
I figured out today that my intake manifold is sucking in air. I guess this might be causing my rough idle?? Its a 98 STS with 100k miles, do you think these problems are related? Is it hard to replace and how much?

Anthony Cipriano
06-27-04, 11:24 PM
How did you figure this? It's very unusual for an intake to be "sucking in air". If you spray water around the perimeter of the intake seal and can hear the water suck in and/or the engine suddenly smooth out then there may be a vaccum leak at a port seal. I'd remove the intake and inspect the seal before doing anything else. If it's a seal then it can be replaced or simply repaired locally with judicious use of RTV.

The other potential source or an air leak or vacuum leak in the intake would be the pop off valve that's located at the front of the intake. Pop the little flapper valve open to see if it's sealing and if some piece of debris is caught under the seal. The pop off valve is replaceable sepately I think.

In any case, a leak at the pop off valve would cause a whistling vacuum leak sound but not likely a rough idle. It would also possibly cause a high idle that the idle air control could not overcome but it shouldn't cause the engine to idle rough unless the leak were huge.

cadillacstars
06-28-04, 12:38 AM
I had a leaking intake manifold gasket, hard start, rough run when cold. best way to diag. remove and inspect. Sorry, but I do not think water should be sprayed around a suspect leaking manifold, may I suggest carb cleaner, propane, or brakkleen. water in intake bad. The "flapper valve" is available separately. personally I like to use propane to isolate vacuum / intake system leaks.

akaz87
06-28-04, 01:35 AM
WEll I found out by putting some soapy water around the perimiter and I was smoking a cigar so I blew it into one of the vacuum lines. I saw the same comming out of the sides of the Manifold. I'm not sure if its the seal though, is it more likley the same is cracked rather then the manifold messed up? How much is the seal to be replaced? or is the seal part of the manifold?

Anthony Cipriano
06-28-04, 12:11 PM
I had a leaking intake manifold gasket, hard start, rough run when cold. best way to diag. remove and inspect. Sorry, but I do not think water should be sprayed around a suspect leaking manifold, may I suggest carb cleaner, propane, or brakkleen. water in intake bad. The "flapper valve" is available separately. personally I like to use propane to isolate vacuum / intake system leaks.

Why not use water? I'm not suggesting a garden hose onto the engine but a spray bottle of water used to find a vacuum leak is far safer than spraying flammable liquids over the top of the engine and/or agressive solvents such as carb cleaner that can take the insulation off wiring or paint off painted surfaces. What exactly is "bad" about using water compared to the other products?

Anthony Cipriano
06-28-04, 12:13 PM
WEll I found out by putting some soapy water around the perimiter and I was smoking a cigar so I blew it into one of the vacuum lines. I saw the same comming out of the sides of the Manifold. I'm not sure if its the seal though, is it more likley the same is cracked rather then the manifold messed up? How much is the seal to be replaced? or is the seal part of the manifold?

I'd take the manifold off and inspect the seal. It's pretty simple to do as there are no coolant passages in the manifold so it just lifts right off. Take out the 10 intake bolts and disconnect the fuel line and lift the manifold up. Possibly there is an injector seal that is cut/damaged that is leaking or it could be the seal around the perimeter of the manifold. As stated, if it's the seal around the manifold it can be repaired locally with some RTV if used judiciously.

akaz87
06-29-04, 03:25 AM
Thanks for the advise. How easy is it to disconnect the fuel lines? This is the only problem that I am getting. I tired to put a piece of tape over the leak and it seems to get better, so there must be a leak in the seal then I think

Anthony Cipriano
06-29-04, 10:08 AM
There's a little tool that you can get at most auto parts stores to release the quick connect fuel line fittings on GM engines. With a little patience you can also release the locks in the connectors manually with a small screwdriver but the tool is sure and easy.

eldorado1
06-29-04, 09:27 PM
There's a little tool that you can get at most auto parts stores to release the quick connect fuel line fittings on GM engines. With a little patience you can also release the locks in the connectors manually with a small screwdriver but the tool is sure and easy.
Ha! Little patience!? It took me a good 30 minutes to do with a screwdriver... I could easily get 3 tabs, but the fourth never made it. Next time I'm buying the $9 kit :helpless:

TimothyNelson
02-07-08, 03:01 PM
I have a 1999 Deville when started the vehicle whistles. I've been told it is the Intake Manifold Gasket, Manifold and Seals. When taken to one shop the mechanic played around with the "flapper valve" and the noise stopped while car was running. I came here and now see that this part may be replacable seperately? If so, does anyone have a part number or specific name for the part? No one I call can seem to find it.

Thank you!

Submariner409
02-07-08, 03:15 PM
You're looking for a backfire relief valve or manifold overpressure valve. I don't have a '99 parts list.....there are two or more versions of the part.

Cadillac dealer parts department.

Ranger
02-10-08, 08:40 PM
I think the Tech Tips section has a parts list as a sticky.

Rafterd
02-12-08, 08:59 PM
My 98 doing the same thing. Checked the intake manifold and foung the bolts were finger tight or less. Tightened them and the problems went away.

Bill

mongongo
02-15-08, 03:52 PM
Amen to that, Found the same thing when doing my starter!!
Idle is great now, no jumping around at all.
And I have freaking 215 thousand miles now.

AJxtcman
02-15-08, 07:02 PM
Is the the area that was leaking?
http://i224.photobucket.com/albums/dd25/AJxtcman/Fiero/intake/intakebackfirevalve.jpg

You can paint it like this.
http://i224.photobucket.com/albums/dd25/AJxtcman/Fiero/intake/Bareintakeonthecar.jpg

ryangreen19
03-24-08, 02:50 PM
A question about that top picture you posted asking if this is where it was leaking. The round insert with the vacuum line tip on it, it is supposed to be loose? , not falling out loose but mine can be spun in either direction a little bit, about a third of and inch or so. Obviously there isn't an airtight seal when this can happen.
thanks

Submariner409
03-24-08, 04:07 PM
That's the PCV vacuum intake, and the fitting should be leak-free. The question is if there is enough space around the fitting seal to allow a vacuum leak.

ryangreen19
03-26-08, 02:38 PM
I guess I wasn't clear enough on my last post, I didn't mean the tip that the vacuum line attaches too, thats fine- snug fit. I meant the larger piece of plastic that is circular in shape that the tip is on. Its about 3-4 inches wide. That is slightly loose on my engine.
Thanks

Submariner409
03-26-08, 03:30 PM
Nothing on that end of the manifold is supposed to leak air as in :vacuum leak. There should be only two ways air can get into the manifold......through the PCV line from the valve/orofice, and past the throttlebody butterfly, depending on throttle opening. The other vacuum taps are static, and terminate at either diaphragms or sensors.

darien99
03-26-08, 07:28 PM
after reading this thread yesterday, I checked my bolts on my intake before I zipped the intake off. Mine were also finger tight.

So this means everyone should check the torque on their intake bolts when they have a spare 5 minutes. Cadillacs are good at hiding vacuum leaks/ignoring them, so you may have a leak and not know it. I did.