1999 Saturn SL1 air filter

Every 30,000 on your car unless you live in a really dusty area then sooner then 30,000. You could always get a k&n direct replacement air filter there reuseable you clean them every 50,000 mile's unless you have a lot of dust then sooner. They let more air in the engine but the engine will be a little louder from that extra air comming in.I have one in my 1999 Saturn and it's a little louder then the stock air filter.