Losing accelerator connection after a bit of time

I am having i20 Magna, due to initial pickup problem means I am losing accelerator connection for few distance later it is getting settling (may be up to the engine heating condition). It is getting jerk while running up to 3 - 4 kms,

Recently complete service has been done, changed the parts by the authorized service center Hyundai, including the ECM, but problem is getting repeated.

I personally feel some sensor problem, please suggest.