My 2000 Ford Focus recently had its timing belt changed, but it was driving smoothly. There was some problem with the fan not turning on but that was a simple blown fuse. But all of a sudden I realized that it has a delay when pressing the gas pedal. When I start it up in the morning it accelerates fine, but after a few drives it starts to get worse and becomes even more unresponsive. Any idea what could have caused this??