In a perfect work, the CIS should adjust for changing amb. temps, but I bet your A/F was adjusted when it was nice and warm out. Now that is cooler, the A/F may need to be looked at again. I'm guessing it's running lean. The air is cooler and more dense. So if your car was adjusted toward the leaner side of things when it was say..July! It is now too lean for December! Just a guess from 3000 miles away.
If it were my car, I would turn the A/F mixture screw an 1/8 or 1/4 turn clockwise and see how the engine behaves after that.
When I am not on my way tot he EPA test station, my car is always on the rich end of things...
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