surging at low speed

Hi. have a 2005 GC 3.3 with about 84,000 miles on it. Lately at a low speed, around 25 mph, the car surges when I holdl the gas pedal steady- speeds up slows down, up down, up down. not always noticable at speeds above around 35 but I sense that it is happening at higher speeds. Also the EC dash light is on most of the time (I understand what this light signifies). What are your ideas about the surging and are the surging and EC light related? Thanks for your thoughts.