Kia Rio - lurching at low speeds

[some bloke]

Hi all, as above, we have a 2010 Kia Rio diesel (my other car is more interesting) that has just started lurching when driving at low speeds in low gear - usually 1&2. We've had it in a garage for checking over but they haven't found a glaring cause or fault code. They fitted a fuel filter and some fuel treatment. We did a 300 mile trip and it seemed to be much better.

It has started doing it again though - any ideas from anyone's experience?