I had a True Flo foam filter in my 04 Ranger which is suppose to increase air flow and better filtration and gas mileage ..was told it was better filtration than the pleated cotton in the K&N type filters....when I brought it in to get serviced under warranty the service manager told me that running an oiled type filter can contaminate the MAF sensor and void the warranty...
After reading on some of the truck forums I seen where some people did have a problem running the K&N type filters and having MAF problems...
I had good milage when I had my True Flow filter in ..But I removed it till I got more info on any problems it may cause...
I have read articles on how to clean the MAF sensor in case you have a problem..but while it is under warranty I will leave it out....
It does not cause problems in the diesals though..go figure....
Here is a video of the filter performance click on product video
http://www.trueflow.com/video.php
Al