My car has been doing alot of chugging when its idling, I noticed it mostly after I put gas in my car. Now it does it constantly. The engine light has been on for awhile now but when I drive it the engine light flashes mostly when I'm accelerating. Took it to a mechanic, the code read that cylinder 3 was misfiring like crazy. Changed all the spark plugs and it's still the same. Could it be that I need a new fuel filter?