Anyone know how to adjust the idle speed on a 1993 (xj40) v12, its sitting at about 1000rpm when warm and im finding it a little tricky trying to fully stop in the snow!!

I always put any auto into neutral when approching a road junction or similar in slippy conditions, even my smaller engined cars (than your V12) only idling at 750 to 800 rpm tend to push the car out with the front wheels locked.
I took the kids sledging up the fell yesterday afternoon and had a tricky job driving down again, neutral most of the way at about 1/2 mile an hour with the wheels in the gutter to find grip. It has not been too bad driving up but late afternoon after few snow showers nd drop in temperature road was treacherous.
Cheers

I would check the idle control valve for it sticking but also note that this is water controlled there is no electrical assistance as in later V12 X300 cars, it is the bain of all V12 engines in the XJS and XJ40 cars, the cure is to clean the bore to ensure that there is no grit causing it to bind.