All Kia models built after 1980 use oxygen sensors.  Your Kia oxygen sensor is a vital part of your emissions control system.  The oxygen sensor transmits important information to your engine's management control system.  Emissions are kept low and your engine is able to run efficiently with the help of your oxygen sensor.  Your vehicle needs to reach and maintain a perfect ratio of air and fuel to perform effectively.  If there is too much air (a lean mixture) or too little air (a rich mixture), your engine's performance will suffer.  This is where your oxygen sensor comes into play.  The oxygen sensor notifies the management computer that there is too much or too little air in the ratio.  The management computer adjusts its fuel output until the ratio is balanced back out.  If your oxygen sensor is not working, this information will not be sent and the engine's computer winds up guessing the ratio.  Performance problems such as hesitation, surging, poor acceleration, emission test failure and poor engine performance can all result from a broken oxygen sensor.