I plan on removing my K&N Air filter and putting back the stock airbox. It simply did not work correctly. The CEL never came off and the car drove sluggish at times. It may or may not be a defective CAI, but my question is - are they really worth it? The horsepower gain is not significant to even mention. The noise they make can by annoying. I did not see any improvement in gas mileage. And from what I've read about CAIs, people just put them in for looks - the rest is just crap. Wouldn't it be better to simply keep the stock airbox and maybe get a better air filter instead? Note: The K&N CAI was designed for my model mustang and it was installed correctly. When called K&N, they said that some cars may not react properly when installing a CAI and nothing I can do about it, sounds like BS, but whatever. A wasted $200+.