I recently kept getting ses lights and my cars kind of old so i tend to ignore em but my dad said he heard a misfire from the exhaust and as i listened to it i hear it as well. It seems like its the same cylinder doing it. It goes "duhduhduhduhduhduhduhDOHduhduhduhduhduhduhduh DOH" (best i can explain it).
My car drives pretty normally minus the ses light.

I checked all my spark plugs and one of them felt a little loose because i could turn it with my hand. I will tighten that once i get a chance. All my plugs are ngk tr55 changed about 1000 miles ago and gapped at .050. My wires were also changed at the same time with taylor spiro pro. All the wires appear to be intact and unburned so i think im ok.

Is there anything else i can do to make sure i dont have any problems and is there any easy way i can make sure my opti is alright?