Ok well I fitted a brand new ISCV and did some more head scratching - I managed to corectly set the base idle. Things were looking promising for an hour or two, apart from a bit kangarooing at times, until the car decided it wants to idle at 2500RPM

If I disconnected control valve the revs dropped to it's base idle. Plug it back in and it shot back up. Basically it has a mind of its own. At the moment it's idling fine, which is making this problem all the more annoying. I've checked the hoses, tried spraying WD40 around areas etc but it didn't throw anything up.

I've cleaned the loom plugs with contact cleaner also.

I've now thrown the towel in on this bloody car.