To be sure I understand the question, are you saying that:
- ignition is off,
- first gear is engaged,
- handbrake is off,
- car rolls downhill in jerks.
Is that correct? If so, that is exactly what I would expect. The jerkiness is caused when each piston arrives at TDC (top dead centre) where compression is at a maximum, hence resistance to motion is at a maximum.
If I have misunderstood please give more detail.