not only mine car but also skill has reported the same thing that his car is smooth on low speed EVEN THE GEAR IS HIGH... means its still smooth if you are driving at 20-25km/h on RPM range less than 1500 and in third gear, car is still smooth (until or unless the coils are fine)...but yes baleno require an extra boost in 2nd gear to gain a steady and smooth drive, but it is something related to the gear ratio...
check engine light makes any difference or not, i shall not comment but i must say every mechanic who couldn't solve a problem tries to convince you that IT MAKES NO DIFFERENCE...almost 99% balenos are on CNG, how many owners have you seen complaining this??? it is something related to electrical issue...could be very minor, very very minor issue, take the car to any scene able mechanic and get it resolved, something a minor issue can cause a big problem, check all electrical grips specially the radiator fan..