So i had a y8 swap in my 91 dx hatch for a while. It ran great but eventually spun a rod bearing. Now, over the last week I acquired a new y8 block and swapped my old y8's head onto that block with oem gasket and ARP headstuds. I also decided to install my turbo kit. Its an IHI rhb5 and Im using the VAFC hack with 450cc dsm injectors. I started it for the first time tonight and it started right up but idles at 3K rpm and slowly climbs higher and higher. My old motor never idled like this before, and I really didnt change much stuff swapping in this new block. What could be the problem, I adjusted the idle screw all the way in and out and didnt change it at all. It starts right up on the first crank and throws no codes but idles horribly like this. What could it be??? Thanks.
-Alex

 

IAC valve?...tps sensor?... ignition timing?...NEVER MESS WITH THE IDLE SCREW. now you are doomed forever, becuase you will never get that screw back to factory spec.

check for vacuum leaks

 

Fix the vacuum leak and it'll idle fine.