For all you poor sods with idle problems (like me!)...
I'm still getting uneven idle on the Cav 2L 16v SRI, so have been speaking to a lot of trained vaux mechanics about it (phoned round all my local garages).
The info below has also appeared before in different places, but this lot is 'out of the horses mouth' as they say...
It seems there is a bog standard list of things they do when you take your motor to 'em with idle problems:
They clean throttle body, disconnect all small breather pipes and make sure they are all perfectly clear inside.
The small stub just below the butterfly on the trottle body is cleaned right out. The hole is only about 2mm (its pipe goes to the top of the crankcase - the smaller of the two) and gets clogged very easily.
The IAC (idle air control) valve is removed and soaked OVERNIGHT in solvent (the entire valve, inc. solenoid).
The Vauxhall oil trap mod is fitted into the big crankcase breather pipe (at the front right which disappears below the engine).
If they deem necessary, then vaux perform another mod which fools the ECU about the actual position of the butterfly (makes base idle speed slightly higher). The mod involves a hole being drilled in the throttle body somewhere by the butterfly and the ECU being reprogrammed to reflect this offset - one that we can't really do.
They wouldn't normally clean the air-mass meter, but reading many posts - others have suggested it.
If the cleaned IAC still didn't perform that would be the next thing to be replaced. But it's expensive. Mechanics tell me it's £115+ vat, but the parts dept reckon it is £159+vat. RIP OFF FOR SOMETHING THAT IS EFFECTIVELY A VAUXHALL DESIGN FAULT!!!
So after all that, you are still getting problems with idling it seems even Vauxhall can't help!
One little bit of advice for others with idle probs on the x20 xev; If the engine idles high (+1000 rpm), get a mate to tap the IAC hard with a screwdriver handle. This would hopefully knock the valve into it's proper position (idle should go OK). This test MAY reassure you that the IAC is actually knackered before spending tons of money on it.