huzaifa,
i assume this problem is both on petrol and cng.
the very first and beginner diagnoses is to check the air filter box,is it sucking air from some where?
To check it spread the tissue papers all around the air filter box,tape them on the roof of air filter hosing,let them hang,start the car,give it revs through accelerator cable on the throttle body and keenly observe the motion of tissue papers(desi nuskha,serves pretty well).
Do it once and report.