The air filter should be checked at every oil change, and replaced when it becomes clogged (a good rule of thumb is that if you cannot see light through it, its too dirty!). Be aware that the 2005 through 2007 Focus does NOT have a replaceable element like the the 2000-04 and the 2008-up, so don't knock yourself out trying to find it on the car, or a replacement filter at the store. But if you wanna have fun with Jiffy Lube, ask them to check it for you, and see if they try to sell you one!!!!!!!
