I had a flex pipe replaced this year. It was after that it seems when these problems started. After getting fuel my 2004 Hyundai GL will spit and sputter when idling or while accelerating to drive, like if I had gotten bad fuel or water in my tank. Now engine light stays on all the time; and starts blinking when I try to accelerate. It spits and sputters when I turn on the defrosters or air. It runs real rough when idling and when I go from idle to accelerate at a light or when I give it gas to go from say 55 to 70 then back down to 60. When I drive at 60 or 70 it runs smooth until I start to slow down. I get the oil changed regularly, Spark plugs were replaced in 2009 and a sensor replaced. Could there be water in my tank? What should I do now?