O2 sensor I think. Or is it coil packs. Hmm, one of them.
is the anti tamper box still on at the back of the engine? (Middle)
cant find a pic, if you open your bonnet, lean over the engine towards the back you will see a large plug to your right, and next to that on the left there is a little black metal box covering the injection computer plug.
Remove black box and have a look at the wires, i bet they are chaffed and shorting out on the black box.
Ive sorted out the same problem as you have described on many 1.2 16vs by throwing the black box in the bin.