Hi i have 2003 elantra gls and the other day my car just started sputtering, idling very rough, stalling, loss of acceleration and so forth. had a advance auto chech my FLASHING check engine light and it was a cylinder misfire in #1. so they suggested to change my spark plugs. well i did and all the sputtring and stalling out stopped but i can have my foot pressed all the way to the floor and the car will barely get to 15 mph in 30 sec. it revs all the way up to 4000 to 5000 rpm's before it would shift. s i canned it again and it said speed shifter sensor. can u help me with this