2001 Ford Ranger Idles high and sometimes too low and dies

I have a 2001 Ford Ranger, and it has 79,000 miles on it. The truck idles really high sometimes and shakes a lot, and if left idling for a little bit it just dies, also sometimes while coming to a stop the truck will idle all the way down and die. My gas mileage is really bad, about 8-10 miles per gallon. I really don't know what could be the problem, someone suggested bad O2 sensors, but it just seems like it would be more than that. I got a code reading before because the check engine light is on and it says fuel is lean/rich in bank 1 or 2. What is your theory behind my problem