check the coils and spark plugs - i had that surging in RPMs that i actually monitored on the digital tach in the cluster, and then in INPA... after cleaning the MAF, the throttle body flap, it came to cyl 5 misfiring... the misfire was not obvious before, only after INPA said it was misfiring... ordered a $35 Bosch coil - and voila!!! everything went normal... so, the brand new fuel filter will sit in garage until i actually will need it...

do you also experience undercut in power? as if you are merging onto freeway, and there is no power to merge you into traffic...