From memory these have a throttle cable. I would check that this is free to move both to open and close. We have seen these cables stick usually because they have been kinked when other work is done under the bonnet and they are moved out of the way. The cable basically sticks and then jumps as the retrun spring on the throttle body overcomes the resistance causing the lurch effect. Check the linear movement of the cable at the throttle body on open and clsoed throttle. If it is the case a new throttle cable is the solution.

Might be your problem