This is a bit of a revival tip but could help users from now on.

I've bought a Ebay ISCV and had the same problem everyone here had, Hunting, High idle speed, etc... Tps and all the rest, aparently, was fine.

What I did was use my original ISCV spring and piston and put it on the new ISCV. After that I put the spring from the new one after the piston and the litle plastic thing after that and then the lock nut. It's idling like a charm now. No hunting whatsoever. I will probably tighten the nut a bit more or extend the nut side spring to get the cold idle a but higher (it's 1200rpm now but solid as a rock).

Just my 2 cents.