i have a 98 protege DX. the check engine light came on shortly after i put gas in, its not the gas cap. i put in dry gas and injector cleaner because i thought it was the gas at first.

the codes reading cylinder 3 misfire and fuel trim malfunction. i replaced the plugs because they were fowled, although they will probably need it again if i dont get the misfire fixed soon. that didnt do the trick. any other ideas on what might be causing the fuel trim to be off?

 

Many possibilities...

Oxygen sensor, MAF, leaks in the intake airstream or the exhaust manifold among others.