MAF cleaner, how to DIY
You might want to do a search, there have been several relevant threads here, with some good information. Cleaning it has helped several people like you who thought their engines were a bit sluggish. I don't think that there's any kind of recommended service interval, except on an "as needed" basis, but I could be wrong.
I just replaced mine; was around $250 at AutohausAZ.



