Yeah there are two wire sensors that need to be cleaned; front and rear.

The get dirty more than you would think even if you don't play in the mud. Its pretty dusty out west so that maybe part of it for me.

I normally check mine when I clean the air filter and about half the time the MAS is dirty so I use the spray cleaner. BTW the air temp sensor is another one that gets dirty so check that one also, uses the same spray that you can normally find at the local parts places:
http://www.crcindustries.com/auto/content/prod_detail.aspx?PN=05110&S=Y