first off give the ICV (Idle Control Valve) a darn good clean, then check for any air leaks 

As said clean ICV first (may need a couple of goes), clean contacts on MAF sensor plug and socket with contact cleaner.  If it still does it try it with MAF sensor disconnected - could be a dodgy sensor.

I would also check what happens when you unhook the plug to the maf sensor see if it runs better

That sounds a very likely cause.

If you go to your Vauxhall dealer they will look up on screen the part to order it in for you while you look at the screen.

There are plenty of maintenance guides on the forum including one on cleaning the breathers http://www.omegaowners.com/forum/YaBB.pl?num=1152598350 . that may have the part number of the item on it. In any case that is a bit of recommended maintenance.

varche

Success!  Well sort of. I found that the third torx bolt housing on the breather bridge had sheared, so the bridge was not secured, hence air leak past the seal.

I reattached the piece of the housing with superglue and replaced the seal as well.

It is 100 times better than it was, but there is still the occasional blip, It seems to me that the rubber sealing fins on the ICV maybe the cause of the small leak as it just seems too loose a fit in the intake manifold.

Can the rubber section be replaced independently of the ICV itself?

If not what would be the implications of using some form of instant gasket to firm up the seal a bit?

Lastly does anybody have an idea on price for a new breather bridge as I'm not convinced of the longevity of my superglue repair?

Cheers

Jim