Duralast Mass Air Flow Sensor
in a year
Not the cheapest sensor on the market, but not the most expensive, and comes with a better warranty than the cheapest ones. Just swap in place of the original - a plug and two bolts, which should only take you ten minutes... unless you have an older Focus, then you have to remove the air duct above the sensor. Adds twenty minutes to the swap time, but not much harder.
What kind of vehicle do you drive? 2005 Ford Focus