P03 misfire reading

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Hi. Each time i accelarate or speed up and the rpm gets to 3.5K, the check engine light turns on and the engine becomes rough. I turn off the engine and the roughness disappears but the check engine light remains lit until I erase the incident w my OBD tool. the error reading says it is a P03 misfire in cylinder 1. What is going on and how can I correct the problem? thanks. t2p