Two common reasons. The first is that it is like any other component and it can just fail for no reason. The most popular reason for malfunction though is people installing air filter incorrectly....
I'm not an expert on this...but my understanding is that a MAS is to an electronic fuel system what a butterfly valve was to a carburated one. It senses and essentially controls the amount of air...
Yes you can by using Mass Air Flow Sensor Cleaner by CRC. Kragen Auto Parts sells it. This is what the Mass Air Flow Sensor Cleaner by CRC looks like (http://www.autobarn.net/maairflsecl1.html) you...