2002 Ford Escort car trouble

Engine Performance problem
2002 Ford Escort 4 cyl Front Wheel Drive Automatic

My car has an unknow amout of mileage. But I have been having a problem with it running. When I stop the car dies or the rpms jump up and down like a yo yo. On cold days she wont start and on rainy days she dies more. However when on the interstate she runs well its hard to keep the speed even with out laying on the gas it is also difficult to get up hillls. You have to floor it and she still only goes really slow unless you get a head start. You can smell gas in the exhaust. I had the computer read but it wouldnt read. I had some one do a compresion test and it tested low. I would greatly appreciate a direction to look into for fixing this problem.