I guess this has been a problem that I just didn't notice until it got bad enough to toss a code and make things interesting.

Last night, my check engine light came on and I retrieved a P0404 code for an EGR issue. Odd thing is, my parking brake wouldn't release and my gas mileage is in the tank now at about 16 mpg.

I manually released the parking brake and drove to my destination, where I then traced the vacuum line for the parking brake release to look for a spot where it may have come apart. The lines were still attached the entire way to the intake manifold. Here's what I noticed, when I wiggled the vacuum line, the entire end plate with the manifold blowoff was moving. I am guessing that my vacuum leak is in that piece.

Here are some past symptoms that should have been a tell tale sign.
1. Parking brake didn't always release.
2. Engine stalls when going down hills at low speeds.
3. Poor gas mileage.
4. Poor idle.
5. Hard starting.

So here's the issue, do I replace the entire manifold, or can I get the gasket or seal that hold that end plate in place? I do see that I must pull the intake to get to it because the power steering unit is in the way.

Thanks for helping.

Don

1999 Deville Concours

Boy, I hate when I do that. I spelled BRAKE wrong as break. There are times when I wish I could break the brake. Dumb, dumb, dumb... too early in the morning.

Don

That overpressure (blowoff) gate uses a spring and silicone ring seal. Sometimes you can pull the whole thing apart and simply clean it. The entire valve assembly is removable, but it's probably a dealer part. There are two versions, so you need the original in hand.

Remove the intake manifold, and because the gaskets are 10+ years old, you might want to have a spare set on hand, but they are technically reusable (spares from NAPA). Double check the integrity of the PCV vacuum tube while you're in there.

I grabbed my spare intake manifold tonight and was looking it over. The overpressure valves look the same, but I can't be certain yet. I haven't pulled my intake at this point.

I am thinking that the rough idle, poor gas mileage, and carbon that blows out the exhaust would be from this vacuum issue. If the vacuum is low, then the fuel pressure value won't work correctly, running too rich, as it think that the throttle valve is open.

I guess I just need to pull the thing and see what all is in there. Good opportunity to give the throttle body a really good cleaning too.

Does anyone know how the overpressure valve body comes out? Pop it out with a screwdriver, or does it unscrew? I don't have my service manual handy, else I would look in there.

Thanks everyone.

Donnie

It turns counter clock wise I believe. When I had my motor all apart I discovered that was my high idle due to a vacuum leak. The gasket to the door was hanging out lol.

While I had the intake off I cleaned the entire inside and throttle body completely. Also cleaned the injectors up they had carbon build up on them.

You can take the backfire pressure valve deal off while the intake is on the motor, you just need a pulley puller specific to the type that is on the power steering pump you will then be able to get to the bolts for the pump. Remove it the use a flat head screwdriver to turn the valve assembly out. I had to hammer it out I used a rubber mallet for good measure to insure not to much shock was put into the plastic. By placing the screw driver on one of the notches on the valve tap it with the hammer counter clock wise. It is a bit tricky to re-install i found you just need to start it properly in the hole with the tabs in the right place and pound it back in the way it came out twith the mallet and flat head.

The backfire pressure valve (if that's what it's called) I got from the dealer for around $35.


Hopefully we are talking about the same thing here. If so then it won't be to hard if you know how to change brakes or spark plugs. The difficulty is about the same.

I believe the later one-piece intake manifolds use a circular valve and spring arrangement, with the retainer cap held in by 2 bolts. You need to work from the open throttlebody end of the manifold.