When checking the stats via the ODB port on the 540 I noticed that my intake air temperature sensor says -40degrees during key on engine off. If however I start her up the sensor returns a figure (9 degrees today in line with the coolant temp). What I'm wondering is whether or not the figure is real or whether its a default value set by the DME given the possibility of the intake temp sensor being dead.

There aren't any fault codes and all other stats are populated key on engine off. I ask as the car runs particularly rough when it is cold and is never entirely perfect when up to temperature. I do tend to find though that on warmer days performance is much improved.

Any thoughts?

Cheers