2002 Vauxhall Zafira engine jerks

Hi, can anyone assist me please? I have a 2002 1600 manual Zafira 71,000mls and the engine splutters at low speeds. Car just been serviced again and previously had the egr changed, throttle body cleaned out, new plugs and filter and it is still doing it. No engine management light is coming on and it seems fine driving above 40mph. It is driving me mad...it will be driving fine one minute and then jerks. If I drop the gear and pick up speed again then it drives normally..happens in all gears.