hi. i haven't been on here in a while. had problems with e-mail. and still am. so i can only get info through this site i now have bookmarked. hope it works. my rpms will not adjust properly when i get my speed up on the hwy. it hesitates and then they won't drop to where they should. when i sit with the car idling in park, it revs up and down sometimes. main things i have replaced over last while is battery, filter, and alternator. would spark plugs cause this problem.?