I have a 1997 F-150-4.6-4x4 with a k&n Filter Kit. The Truck has 87000 miles and has started to run rough and stall. I plan to clean the o2 senors as stated in some of the other posts. The other symptom is the gas cap makes a grunting noise. When I open the cap air rushes in and the idle smoothes out. When the gas tank has 1/4 left the gas gauge reads full. Thanks for any help.