Jerky in first and second gear

I just bought this vehicle. There is this jerky and the car trembles a bit while accelerating in first and second gear. I brought it to a mechanic who state that the "throttle sensor" is the issue. He mentioned he has cleaned the sensor and now first gear this issue does not occur only in second gear. The only way to avoid this issue is to delay the release of the clutch in second gear. I have brought the car to the local Kia dealership to confirm the throttle sensor issue, they have plugged obd2 and all checks is fine. So we went for a test drive to confirm the issue and the mechanic acknowledge but the mechanic told me they've had this issue before and they could never solve it. So I am stuck. Has anyone had this issue before?