I have a 87 XE V6, I had left it idling for about 15 mins to warm it up, and i noticed some gray smoke from the exhaust and some black stuff on the snow below it.It has also been really cold here the past week (-40 to - 45) and i was wondering if it has anything to do with that. it has always done about 16 miles to a gal, but past in the past few days the mileage has really dropped below 10mpg. Do i need to be worried? what could be the problem? any help is appreciated. thanks.