I have always had this problem, it could be a few things.

I suspect it's your TPS at fault, in your case you can unplug it, as a test, and see if this makes any difference, if so then you need to look at calibrating the TPS etc.

When you say you changed the ISCV, I suspect this will be a pattern one off the bay etc?

If so these arn't that good, I have one myself and whilst it got rid of my hunting problem it run very fast with it, so much so I reverted again.

The reason being is the incorrect springs being used, you can get them to work but they need a lot of playing around with, I have to do this with mine.

Martin