On my 1991 Plymouth Sundance RS 2.5 TBI, I bought a K&N air filter from Autozone (they had to special order it) and have been running it for a little while to see how it performed. K&N claims that you get better air flow with them.
Unfortunately, during the time I've been using it, I haven't been having a great experience with it. When I pulled the air box off during a recent oil change to check the air filter, I took the filter out and noticed that I could ACTUALLY see through the little porous holes. Ha..makes me wonder about something. Then..I noticed that there were particles of dirt inside the air filter housing assembly in the center part in the rift by the throttle body. Hmmm.....makes me wonder if the K&N is actually letting dirt through. By Golly I don't want that crap blasted right into my TBI!!! Also, to my dismay, I noticed that there was reddish oil, which appeared to be K&N air filter oil, all over the air filter housing and a little bit on the throttle body and its gasket!!! Ahhhh!!! God knows whether that oil got into my engine or not!
Overall, I'm not very happy at all with this filter that K&N put out! So, I decided to go to NAPA and get a regular air filter and use it instead. I now go to NAPA for parts instead of Autozone because I was told that AutoZone hires people from the street, and Advance Auto doesn't seem much better than AutoZone. Anyway, there doesn't seem to be any difference in performance between the NAPA and the K&N. Overall, the K&N apparently doesn't flow much (if any) better than an ordinary filter.
I'm not using a K&N air filter in my car ever again.
Anyone care to chime in on your experiences with K&N air filters good and bad?