It seems the intake blow off valve is being silly. duct tape it up, make boost. I can't seem to find one except used on ebay.
I am going to delete it i think.
All it does (on gas engines) is prevent the compressed air from from bouncing off the throttle plate when you let off the gas, and running back to the compressor wheel stalling it. Diesels have no throttle plate to bounce off of. No way for the air charge to bounce back.
I assume it was used to limit the boost to 12 psi. Later intakes don't have one, but they are fitted with a wastegated turbo that limits boost.