Ok, I believe I have had this problem before, but sometimes it seems to dissapear, I didn't thoroughly check this problem before, I would just quit LFS for the time being, as I assumed the problem was overheating of my graphical card (Radeon 9700, but the same issue appeared when I was still using the 8500) due to........ hotter weather..
The issue I'm having is that when I use pedals, the FPS drops to 15, or rather, the game stutters(bursts of no frames I suppose) about every 13 seconds. I usually use 3 wheels, one DFP for steering, two microsoft SW's for footwork. I tried using each of them individually (even hooked up the DFP's pedal set) and every time the same issue appeared. When I tried LFS w/o pedals(with just the DFP, no pedals) the FPS kept stable. The same happens when I select "Buttons" as throttle/brake control, I get stable FPS.
This is probably one of those unsolvable problems again.... I always tend to have those... makes me unable to ever participate in events, quit games, leave societies, lose friends.... *sigh*
Any help (and compassion) will be greatly appreciated!