2000 Deville 4.6 dohc vacuum leak

I have a 2000 Cadillac DeVille with the 4.6 DOHC V-8. Has a bad vacuum leak, with a stethescope it sounds like it is under the plastic intake manifold between the manifold and the throttle body. Can't make up my mind if it is the rubber boot that joins the two, or if it is the manifold itself. Are these manifolds subject to crack or break? Or can the boot be bad?

Have you measured the vacuum? It sounds like the intake gasket near the TB is bad. I haven't heard too much of the intakes breaking or cracking, but anything is possible!

Haven't measured the vacuum, but the brake booster doesn't work properly, and you can actually hear the hisss without a stethescope, but with it you can run it down between the intake and the throttle body and towards the bottom of the boot, it is really loud there. Guess I will take the throttle body off tomorrow and work from there. It's got to be either the gasket or the boot.

This leak is so bad the engine just will barely idle.

Which boot are you talking about? It's not the brake booster hose is it?

There is a rubber boot (or connector) between the plastic intake manifold and the backside of the throttle body. Appx 3 - 4 " in diameter. Has three bolts that attatch it to the back side of the throttle body and 1 large screw clamp that is on the manifold side. Apparently this boot has a hole in it now, and is leaking badly. The local gm dealer is supposed to have it for me tomorrow. At that time I will also look closely at the intake manifold itself.

It definitely isn't the brake booster. The hiss is very noticeable and makes the engine idle extremely poor, if it will run at all.

I guess I never noticed that boot there before. How the heck does it get a hole in it though?

You tell me and we'll both know. I'm still waiting on parts to get in. The plastic intake has to come off to get to it, and I had to order the gaskets that go with it. They are supposed to be reusable, but knowing my luck if i try, they won't hold, so I'll just put them in new any way.

It's fixed. The rubber boot had a large crack in the bottem side, ao a new boot and new intake gaskets has the car running like new.

It's fixed. The rubber boot had a large crack in the bottem side, ao a new boot and new intake gaskets has the car running like new.

That's great to hear! Enjoy your Caddy!