I had the engine system cleaner brought me, because with my Golf 5 2.0 TDI (PD) had made a sometimes quite violent jerks of the engine at idle bemerktbar (especially when waiting at traffic lights). After some hints on the Internet that can probably be, among others, dirt in the pump nozzle elements. By adding this additive to the bucking at idle has indeed significantly reduced. However, it is not entirely unlikely that it increases again in the future fill ups. A long-term effect is therefore likely to be expected. For me it seems at least bucking again increasingly occur (without additives).