Won't be ISCV if this were the case it would not start at all without more air, I ran mine with ISCV disconnected as had problem, just used throttle instead when cold.

As said do the wiggle test, wherby "Wiggling" CPS connector with engine running as these do suffer poor connections on the car side, though it sounds to me like a fuelling/ignition problem as it's when you OPEN the throttle, check the fuel filter.

You most likely have a T34 turbo, most likely with a .48 exhaust housing, very good turbos!, easiest way is to look at the inlet hose I think it's something like there smaller at the filter end can't remember off hand it's a T34.

Martin