The check engine light is on because the ECU detected a fault. So the first thing to do is read the code stored in the ECU. Then reset the ECU and see if the check engine light comes on. When the check engine light is on, the ECU is in default mode which means that many of the inputs that makes the car run good are ignored. Autozone, I hear, will hook-up a reader to determine the stored codes. When you have that info, come back here and tell us what you found.