The misfires might be caused from a dirty/defective Mass Air Flow sensor.
Purchase an aerosol can of MAF sensor cleaner and try cleaning the MAF sensor. If this shows no improvement, then a scanner should be connected to the computer and then the vehicle taken for a drive. On the scanner observe the throttle position relative the mass air flow. So for example if at 100% wide open throttle the MAF sensor reads 80% mass air flow, the problem is with the MAF sensor.