98 Isuzu Rodeo Engine trouble

I have recently aquired a 98 Isuzu Rodeo and am having some engine problems. Every now and then whilst im driving my RPM's will drop about 200-600 and hop back up to what they were originally all in the time frame of less than a second. This happens while traveling at all speeds so i dont think it has to do with the transmission. The car idles fine and everything else seems to be in good working order except for this. I believe i have a misfiring cylinder but am not sure. Anyone go through a similiar situation or have any recommendations, thoughts, etc?

Have tried reading through the FAQ's and searched previous posts? There have been several RPM related posts lately.