guyz i swapped a z6 head on my b7 and now it idles at like 1500 to 2000 rpms, what have i done wrong?

 

Be thankful yours idles, lol. I spent quite a bit of time just trying to get mine to run. I'd first start with making sure your idle adjustment screw is set to where it should be. What happens once it warms up? Still the same?
I'd also check out your timing, could be something as simple as the ignition timing being off and causing some funky idle conditions. Speaking of that what distributor are you using? 90-91 Si?