Penumbra: Black plague FPS issues

[plutomaniac]

If the game is from steam do a file integrity check, there might be corrupted files causing errors and thus lags.

Apart from that, I had this issue too back when I was playing Penumbra. You just need to leave it for 1 minute or so when entering laggy rooms and the fps will rise. It's like it needs some time to settle in some occasions.