for those not wanting to fiddle themselves
If you tell your dealer your car feels like its down on power, they will check, and replace, the MAFS for you- just be sure that you are within the maintenance period or have the dealers good graces. 2 MAFS can cost about $700! The process of opening up the airbox/ getting to the MAFS is not too bad, but if you are nervous, you can just go to the dealer. I think every 3 years one should get this checked.