Winter VS. Cougar (Vaccum brakes fail and car accelerates)

I have a 2000 v6 Mercury Cougar. When it got chilly here (0 to -10) the car began to shake and it does not like to idle. When idling the Rpm would move slightly. Driving it it was alright once it warmed up. Then when it got really cold (IE -15 to -35) the car is just not drive able. The rpm is moving constantly between 1 and 3. The lights on the inside of the car dim and then light up. The car seems like it will violently shake to death and stall. Worst of all the vacuum brakes stop working and you are virtually unable to press down on the brake.

I had someone look at it and they said that the oxygen sensors in the car were not working and that my "hub" was clogged. Also there were some issues with the idle air control? I'm not sure what any of these mean. But, they were fixed and the car was working fine. It was about -25 that day. It also worked well the next morning. There was also a humming noise but, it didn't seem to be caused by anything.

Then, however, upon starting my car after work it began going crazy. The rpm would fluctuated from 1 to 3  and back down and the up again. I let it warm up in this state and test drove it around the block. This time the car seems to really want to go. It accelerates by itself drastically (IE going from 20 km/h to 40 km/h) with my foot off the brake. Again, the brakes became very difficult to push down.

Please help, thank you.