I have just read this in RAVE regarding the TD4 auto box, is this the jerk your looking for?
Must admit mine does not feel like it goes into neutral when all the conditions are met??
Electronic Automatic Transmission (EAT) ECU Strategy
On automatic gearbox models, the EAT ECU implements an idle neutral strategy, which is part of the fuel reduction
strategy. Neutral is selected, reducing engine load and fuel consumption, when all of the following conditions are met:
1. ECM confirms engine at idle.
2. 'D' selected on gear selector lever.
3. Foot brake applied.
Should one of these conditions change, after neutral has been selected, 'D' will be reselected automatically.
When the EAT ECU requests, via the CAN bus, a reduction in engine torque, the ECM reduces engine torque by
cutting back fuel delivery. This ensures smooth gear changes throughout the engine speed and load ranges, and
reduces exhaust emissions.