S4C with LSD should all be the same I would have thought, EK9 or EK4 (JMD) same gearbox.
NZ prices I have seen are equivalent of 350 - 400 pounds approx.
Check your O2 sensor, New O2 sensor fixed my problem with hunting idle.
Makes sense that it doesn't do it when cold as it runs rich until warm.
I got this one
http://www.amazon.com/gp/product/B000C5SG40?psc=1&redirect=true&ref_=od_aui_detailpages00
Best deal I could find