3.8L 2004 Bonneville whistle/vacuum leak
 

Engine has been whistling when the engine is first started for a few weeks now. Seemed to go away after the engine was warm.
Finally able to determine the whistle is a vacuum leak emanating from the line that originates at the rear of the intake plenum in the line running from the plenum to the power brake booster. Nothing else in this vacuum line.

Tried to remove the piece that snaps in to the plenum, broke off the small orfice on it. Was able to repair that with a screw and sealant. Would replace it if I could find one.

This piece that snaps in to the plenum is loose when snapped in to the plenum, suspect it is the problem. Hose and check valve seem ok, there was a good vacuum in the booster when I removed the check valve.

I can find no part number anywhere for this part, or the silicone gasket it takes. This is what I need help with. Tried to use an 'O' ring from a kit but the size is too far off.

Any ideas where I can get this part number, and find a replacement?

thanks,

I found the part your looking for, but its part of a whole intake kit...

Item Details

That is the problem I"m having all I found was the complete kit. Maybe a dealership can help me. I can't get to one during the week so I guess I'll have to wait until next Saturday am.
I have replaced the plenum, don't normally throw out parts just in case I may need them but in this case I don't have the old one.
May try to find a new silicone gasket but that means I'll have to remove it and use another vehicle, that part is easy the hard part is finding a place that may stock silicone gaskets.

Mike,
It took this long to verify where the whistle (vacuum leak) was coming from. With the engine at idle and the closeness of everything it was a challenge. I have finally determined that the cause is the gasket between the (upper) intake plenum and the lower intake manifold.
The leak is located between the middle rear fuel injector and the vacuum line that feeds the brake booster. Found it by putting my fingers up against the plenum gasket. Could feel a vacuum and the pitch changed as I contacted the area. It still comes and goes as it always has.

One of the strangest things I've had on this or any other car.
The plenum is secured, the fasteners are not loose, looks like the fix is to change the gasket! I want to know what the gasket looks like in this area anyway.

As an aside. During the time I was trying to locate the leak I thought the MAP sensor area could be the problem. During this check the MAP gasket was actually sucked into the plenum. Very odd situation. Put a ty-wrap around the top of the piece that holds the sensor in, forcing it down. Never would have thought that gasket could be sucked in to the plenum.

rockauto has dorman 615207 with all the gaskets and orings for that sensor for 35 or you can get dorman 615180 and get the whole manifold with everything pre installed, and the new egr design tubes for 75. i did my lower ones while i was in there and the aluminum elbow, because those are the guaranteed problem areas on any 3800 and if you do the new design ones you wont ever have to worry about oil leaks or coolant leaks into the cylinder and hydro-locking the engine. that and not changing the oil are the only two things that can take out a 3800.

https://www.gmforum.com/mechanical-1...2005-a-304071/

The aluminum elbows have been in for about a year. The original plenum was changed before I bought the car at about 36k. Had to change it again a couple of years later to the newer design.
Leaking gasket showed up about 3 months ago, first thought it was a bearing until i noticed it slowly died when the engine was shut down and the bearings had all stopped.
Engine has 193k on it. Change the oil about every 6k. Used the same oil change mileage for my old Pontiac 6000, sold it running with 265k on it.
Miles are mostly highway, go between 600 - 900 a week.

you could get away with just the upper gasket set, but you are going to need the one with the tb, orings and such because if its going in one spot the others are likely hard and brittle too. i would also do the lower gaskets as well if never changed to the aluminum framed ones. it was the second time i did my intake too, they didnt have the new design the first time i dont think. mine has almost 200k now. i dont feel good unless i get at 200 out of my cars.