Never have i ever had any issues like this in lol.. It's %%%%ing unplayable to be honest.. I have cleaned my computer off from dust in and out, I've followed riots fps guide (remove unwanted programs, terminated programs i think might use a lot of power, reinstalled LOL, scanned my computer for virus, updated my GPU driver, set windows to best performance, defrag) and I'm at the point where i wanna try to reinstall windows but I'm 99% sure it wont help. I'm just happy I'm not alone with this problem.
I can set the graphics to low, move the map to a dark corner and get 30fps, wait a few seconds and get 60fps.. If i wait more it goes back to 30fps.. Even in teamfights the lowest I've gotten to is 30fps, lucky me am i right? to get 30fps in lol.. Seems to happen just as much in a dark corner as in a teamfight.
Tell me your story and riot might actually open their eyes and look into this..