idle gets low when engine warms up

I have a 2004 Hyundai Sonata manual transmission. It is idling low and rough when the engine gets warm (it is fine when the engine is cold). It also cuts out if I am accelerating and the rpm's are around 2000 or lower. The check engine light is on. The car is not overheating but if I am sitting in traffic for awhile it does sometime rise to mid-line and slightly above. I have been putting some fuel injector cleaner in the my last few fill ups which I thought was helping but it is not consistent.