Originally Posted by Greg in France

Yes the V12 ECU does alter the fueling for coolant temp, and very slightly for air temp. But this is a far less sensor-driven system than modern ones are.

Originally Posted by VancouverXJ6

Reminds me of a mod my mechanic told me about, a dial switch fitted inline to the airbox sensor which could make a stock XJS lay down rubber treadmarks from a dead stop if 'turned' up high enough. I always thought the air sensors were a minor fuel trim but he swore it could crank the power up if you alter the signal output correctly.

Originally Posted by Greg in France

Warm air is less dense than cold. At tickover/traffic speeds (and I am quoting Roger Bywater here) warm air gives better fuel efficiency because (I think I remember correctly his point) you get better fuel droplet evaporation into burnable fuel vapour. At higher revolutions, this is less of a consideration because the airspeed down the inlets, and the swirl and squish in the cylinders etc etc ensures good fuel vapour conditions even with cold air.
Cold air is theoretically better for power, as cold air being more dense means more oxygen molecules per cylinderful of intake air. So at higher speeds cold air is better, at lower speeds cold air is less fuel efficient. If you go out on a crisp below zero winter day, you will notice sharper bark to the exhaust, and sharper engine response than in high summer.
I seem to recall that the difference in max BHP between zero degree C cold air and (say) 35 degrees, is about 10%.

This has nothing to do with O2 sensors etc etc, whatever state of tune the engine is in it would have the same effect.

Yes the V12 ECU does alter the fueling for coolant temp, and very slightly for air temp. But this is a far less sensor-driven system than modern ones are.