Many users reported a (frames per second) after installing the 1.8 patch. This was a disaster for competitive players on older laptops or low-end PCs. The Steam overlay and friends system added overhead that the original game wasn't designed for.
Ensure your game is updated to the official first (the last official retail patch). Download the v1.8 / CoD4X client files. Place them in your game directory and run the installer. cod4 18 patch
In 2008, Infinity Ward released patch 1.7 for the PC version. This was the final official update for the game. It fixed a crucial DirectX error and smoothed out a few multiplayer exploits. For the average player and the competitive leagues (like CEVO or CAL), version 1.7 was the gold standard. It was stable, secure enough for the time, and the version on which the competitive "Promod" scene was built. Many users reported a (frames per second) after