here's the story..
About a week ago i stop to get gas for my car.. i drove it to my girl's house.. after a few hours with my girl, i decided to go home. when i started the the car, the noticed that my check engine came on

.. i figured that it was the gas cap and drove home.. i tighten the gas cap when i got home.. so the next day the check engine light was off.. i thought everything was fine.. the next morning i started the car and the check engine light came back on.. For the next few days the check engine light would go on and off everytime i start my car..today i went to my friend's car shop. he did a scan and it read that i have 3 misfire.. i'm guessing it 3 out of the four cylinder... he told me that he reset it?

as of this momment i am stuck!! i dont know what to do!! my car only has 19,900 miles on it. i just dropped in a k&n air filter about 3 weeks ago.. could it be my spark plugs?? or is it something wrong the the cylinders??