The Nissan Path

I heard with some engines if the air / fuel mixture isn't right it can make fuel mileage worse. So with a that being said...has anyone every removed a CAI and replaced it with the stock air intake but with a K&N or some other brand of high performance cleaner? There may be a chance I'm over thinking this one..Thanks

I doubt you'll see much of a change in MPG regardless of which way you swap. Lower restriction air filters like K&N really don't have much benefit over a conventional paper filters except at high RPM. Most people don't drive at high RPM most of the time unless it's a race vehicle. Under normal driving conditions, an engine is only going to pull in a certain amount of air and either type filter is more than capable of handling that amount. As for as cold air induction, technically the original factory air cleaner is cold air induction as it pulls its air from outside the engine compartment. While K&N filters may offer reduced air restriction at high RPM and better performance, they also have their downside in that they let in more dirt (than a paper filter) and the oil used to coat the filter can contaminate the mass air sensor's hotwire and cause inaccurate readings.