Ford fiesta '54' 1.4 petrol zetec juddering?

Can anyone help me with the following? My fiesta is getting stuck at low speed when pulling away from junctions or going at low speed or up steep hills, it then judders violently and after a few metres like this decides it's going to zoom off. The Sandicliffe Ford garage first said it was the hego sensor but when i took it in for it to be replaced they then decided there was nothing wrong with the car or that it could be so many different things they werent going to spend my money on cures they werent sure about. They told me to thrash it a bit and asked me if i would like a driving skills course from their technician, making out it was my driving! But on investigation from friends who have Fords, it seems a problem they have all had at some point which they have either decided to live with because no garage in the area can fix it, or after several thousand miles it has just gone away. However, it's really dangerous, especially pulling away onto roundabouts or pulling away in traffic jams if it decides it's going to zoom off into the person in front. I am rapidly losing confidence in a car which has always been so reliable for me. It's going to cause me to crash.