when i had this problem i took my K&N off and replaced the original then took it to my local dealer. Luckily my friend turned out to be the mechanic and he said in the end they found out that it was the MAF sensor which is the sensor that plugs into airbox. They are very very sensitive! He mentioned that any slight knock on the sensor can damage it! Honda replaced the MAF sensor under warranty thank god! lol. I havent put the K&N back on now because of the sensors sensitivity! oh well my civic has opened up a bit now from new so im happy with the genuine sound!