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[Debs.]

Plucked-up courage to tackle a breather-bridge clean; they were indeed very 'cruddy' and near to being blocked.
There was also significant crud lying down-low in the throttle body butterflies: all parts have been cleaned/flushed out.

Most all of the job went well except for the large (kind-of caged?) o-ring underneath where the bridge sits down into the plenum/manifold.....anyway, that o-ring was toast and fell to pcs as I lifted the breather-bridge up.

I had a 'plain' o-ring in stock that`s a perfect tight-fit and have used that: would there be consequences for not using the original 'caged' type o-ring?  :-/

Actually, the old large o-ring must`ve been toast for a long time as the engine is much quieter now and the 'hissing' which characterised the (bonnet-up) idle previously has now gone.  

[TheBoy]

Plucked-up courage to tackle a breather-bridge clean; they were indeed very 'cruddy' and near to being blocked.
There was also significant crud lying down-low in the throttle body butterflies: all parts have been cleaned/flushed out.

Most all of the job went well except for the large (kind-of caged?) o-ring underneath where the bridge sits down into the plenum/manifold.....anyway, that o-ring was toast and fell to pcs as I lifted the breather-bridge up.

I had a 'plain' o-ring in stock that`s a perfect tight-fit and have used that: would there be consequences for not using the original 'caged' type o-ring?  :-/

Actually, the old large o-ring must`ve been toast for a long time as the engine is much quieter now and the 'hissing' which characterised the (bonnet-up) idle previously has now gone.  

Only about £1.20 iirc, so may as well fit proper one...

[Matchless]

If the O ring is a good fit then you should be OK as far as air leaks are concerned but you will have upset the multi-ram working because part of the fancy seal is there to keep the left and right intakes separated.
If you get a new seal, dont forget to unbolt the throttle body before trying to remove the breather assy. You might also need the O rings for the two breather pipes- throttle body, they only seem to survive removal once or twice.

[MutantCav]

Is this just on 2.0 or the v6 too?? I have the hissing noise under plenum with bonnet up and the car runs really rough...its an air leak I'm sure but need to work out where and how to fix it...

[Tab]

mine's making the same hissing noise, i got told about it being the o-ring for the breather brdge.
it runs ok must be a common problem.

[MutantCav]

Well mines running like crap, idling rough, struggling to accelerate (although this varies and is fine at higher revvs plus improved by having sports mode on) and fuel consumption is way high...no one else with this problem seems to have rough running though so maybe I have another issue too??

[MutantCav]

To get to this weird o ring I have to get the plenum, fuel rails and bridge off (the bridge being the black plastic thing with the red gaskets??) is his right??

[Debs.]

Is this just on 2.0 or the v6 too?? I have the hissing noise under plenum with bonnet up and the car runs really rough...its an air leak I'm sure but need to work out where and how to fix it...

Mine`s a 2.5 V6 Chris; it`s made that idle-hissing noise for the 2 years I`ve owned it....the 3 o-rings (2 small, 1 large) were really loose and floppy (the large-one fell apart) when I disassembled the breather-bridge from the throttle/manifold so I`d say they hadn`t kept much of anything in (or out) at all.  

I had an assortment of plain o-rings to hand so I just found some that fitted tightly (rather than worrying about them not being the 'real' Vx. items)......all the hoses seemed tight and clear, so the idle-hissing sound was the o-rings for-sure because the hissing is no more!  

I used this as a visual guide: http://www.omegaowners.com/forum/YaBB.pl?num=1152598350

[Matchless]

To get to this weird o ring I have to get the plenum, fuel rails and bridge off (the bridge being the black plastic thing with the red gaskets??) is his right??

We are talking V6 breather bridge (the bit with Ecotec on it)
You just pull the intake pipes away from the throttles, loosen the throttle body bolts a good few turns, lever off the 'Ecotec' cover and undo the bolt hidden underneath, disconnect the breather and vacuum pipes at the back and the breather bridge will then lift up and away from the throttle body, revealing the seal underneath.

[Matchless]

Anyone chasing an air leak and eliminated all the usual places  but still poor vacuum
I had this recently and stripped it all down to the intake bridge again. I discovered that the threaded brass inserts in the intake bridge were slightly proud of the surface and were stopping the intake manifold sealing properly. Filed the excess brass off and intake vacuum improved from 17" to 19.5"

[albitz]

is there a list anywhere of the o rings needed to remove/replace the plenum , or do they come as a kit? :-/

[MutantCav]

Dont suppose you would be free sometime to show me matchless?? I have already swapped over the plenum/throttle body and egr as a whole unit and the problem still occurs...should changing all that have fixed the issue in theory if its the breather/bridge orings???

[Big_Roger]

Hi
The "caged looking O ring" in centre of plenum you are refering to is Vx part no: 90467543

They come in a pack of 2   £1.60 + VAT  bought some last week.

For info the O rings do not come in a kit

Roger

[Matchless]

Well mines running like crap, idling rough, struggling to accelerate (although this varies and is fine at higher revvs plus improved by having sports mode on) and fuel consumption is way high...no one else with this problem seems to have rough running though so maybe I have another issue too??

Chris, post as a new thread. You would seem to have more than just O ring problems.

[MutantCav]

Already have mate...but there is a definite plenum airleak and its a good place to start???