well the story so far, went out today, we did about 150miles up the Yorkshire coast, car with the K&N 57i on felt quicker and the revs where better at idle, BUT some times when you let off the throttle it would almost stall, this has never happen before, so when i got home i put my standard air filter back on, and the problem has now gone along with the £88 i paid for the K&N, any advice????