i'll take a stab. there is an iat (intake air temperature) sensor that plugs in to the intake manifold. this is where the computer gets it's air temp info from. if it is unplugged, shorted to ground, covered in goo, or just failed, it might be sending a signal so far out of whack that the computer is just defaulting to a minimum value (-40). the iat sensor is #17 on the diagram below:
Intake Distributor