Hi Dan

I had mk 5 ZS for 4 years. Great wee car apart from the chronic rust problem, but hey it is a ford after all.

Mine started to hunt for revs on idle and when coming to a standstill would hover for a second then drop just after you stopped.

This seems to be a common problem and the Idle Control valve getting sticky was often the culprit. Clean it with carb cleaner and see if that helps, its only two bolts IIRC. I ended up replacing mine which did help the hunting for revs. I also remove the induction kit that I had put on for the standard airbox (it shouldn't have any holes drilled in the bottom btw).

One thing I did notice was very weird was that when the gearbox speed sensor was disconnected the fault completely disappeared. I was told (no idea if true) that this had the effect of feeding the ECU default sensor readings, but which sensor was at fault I didn't know. A lot of people ended up replacing all sorts of parts from donor cars and it can be a lengthy and expensive process.

Good luck mate.