Cold weather rough start / all year rough idle

I have a 2009 manual transmission hhr with what seems to be an unsolvable problem. I live in Detroit wvuch as you can imagine gets very cold. As the temperature drops, my car gets harder and harder to start. When the car turns on for the first time in hours (say overnight), the rpms will bob up and down dramatically for about 4 times and then sit where it is supposed to. Now that it is December, I have to keep my foot on the gas a little bit to have it even start without dying on me. To make things even weirder, throughout the year, not just Summer, the rpms will sit a little low at idle after about a minute of driving. If I sit at idle for too long, the CEL will come on, but then disappear the next day. I am desperate for an answer so any help I can get would be great.