The engine on my friend's 1985 wagon suddenly started racing on him, and his mechanic told him that he needed to change the computer. My friend wasn't too specific with the details, but why would the mechanic prescribe a replacement computer? Do they had a bad history of failing? What is the Air Mass Meter do for the engine? What effects does a bad AMM create? Should they be replaced together?

Please note, just last week the car wouldn't start. When he pulled the plugs, they were drenched in gas. The mechanic replaced the distributor, the "main fuse", plus regular tune-up items (wires, cap, rotor, plugs, air filter). The car ran great until today...