well if it stays cool when you're driving, and it overheats when you stop...thats obviously an airflow problem. If you have access to a high speed/velocity industrial fan, try idling with it blowing through your radiator. If both hoses are hot and the radiator has no spots on it that are obviously cooler than the rest, and you're not losing coolant...i'd say its deffinitely airflow. Check oil for coolant and vice versa though man...headgaskets on the KA's love to blow.