I don't know if the 1.3 JTD has a lambda/oxygen sensor.. but if so, that's a possible cause.
The lambda sensor has a heater circuit to heat up the sensor at low rpm, when the volume of exhaust gas passing over it is insufficient to keep it at the operating temperature required for it to work correctly. Once the revs increase, the temperature of the exhaust gas keeps the lambo hot enough to operate normally, so the heater circuit is turned off.
The heater turns off around 1600-1800rpm although that probably varies for different engines. If your lambda is on the way out, then as the heater assistance is withdrawn, it can stop operating optimally, sends an incorrect signal to the ECU which would then trim the fuel based to what it thinks is happening and so you get the hesitation.
If you have a ECU scanner, you might see a lambda fault logged... although error codes only come up when the sensor is operating out of range, rather than just badly but still within range. If you get the shakes more when the engine is cold, and your fuel consumption has taken a -10% hit, then swapping the lambda is a good bet.
Ralf S.