I have had this with mine ever since I had the car, in my case I am sure it's the ISCV, I did try another Ebay job which stopped the hunting but it idled way to fast, it's to do with the incorrect spring rating and you have to sod about changing them around etc with the ones from the other valve.

In your case, I suggest you look toward your TPS, check the output!

Also is your base idle set correctly?

I assume it's the Escos in your siggy?

Martin