A faulty mass air flow sensors can cause numerous problems without setting off a check engine light. Owners typically do not notice a decrease in performance, driveability, or fuel economy until the problem becomes severe. By replacing a faulty MAF drivers notice improvements in performance, idle, and fuel economy. It is not uncommon to have to replace a mass air flow sensor every 1-2 years especially on cars that have been modified.  

Replacing MAF sensors is one known solution for "lean" or "rich" engine codes.