1998 Hyundai Accent Running Problems/Unset readiness monito

Just bought the Accent from a friend. It was running bad which is why he sold it. At idle on cold start it seems to run smooth. And at first it would rev fine without heavy load. When placing the car in a gear and proceeding to accelerate the car would start breaking down. The plugs and wires have been replaced and nothing changed. The car had been sitting so I ran out the old gas and put new fuel in it. It seemed to run better but still not good. The other factor is that I put my scanner on it and there are no pending codes, however there is an unset readiness monitor for the catalyst. Both of the o2 sensors seem to be reading right. So maybe the cat? Or would this seem like something else? Oh and my cooling fan doesn't come on.