Engine Performance problem
1998 Nissan Altima 4 cyl Front Wheel Drive Manual 138k miles
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my check engine light is on, so i had it put on a machine to find out the problem. turns out my 3rd cylinder was mis-firing. so a mechanic suggested a tune-up, which i figured i could do myself. i changed the spark plugs, wires, distributer, rotor. i am still getting a mis-fire and am not sure what i can do next.

generally i use good parts but figured i could get away with purchasing those parts from autozone. please advise what you think the problem could be. thanks for answering my questions.