I have this car for over 4 yrs and only completed all the necessary maintenence, such as oil changes. For two day, I noticed that the engine is running abnormal, with idle higher then normal; approx. 950 rpm. Normal rpm is 750. While driving my car I also noticed the engine idle races to 1300 rpm then slowly comes back to approx. 950 rpm, each time I come to a complete stop. I drives my car often today and well aware that it's not normal. While stopping at an intersection, Suddenly the check engine light comes on. I could feel the engine idle lower to its normal; 750 rpm. I immediately shut the engine off and turn it back on because I thought the engine shuts itself off but I turned the engine back on and the check engine light maintain lid. I've checked the gas cap by loosen it and tighten it back up. I read the manuel book and it recommended to have it check by the dealer and avoid further operating my car due to more damage if driven. What do you think the potential problems?