What is this intake valve Nissan TD27T Terrano

[jetskiwi]

Hi Guys
Can anyone tell me what this vacuum valve does, that's in the intake circuit of my '93 Terrano TD27T





The two vacuum hoses into and out are blocked by ball bearings (modified by previous owner?)
I've had low power until removing both tubes and replacing (still blocked). I was going to run some new vacuum hose as they're splitting and I thought prehaps a vacuum leak was the problem. But now they're blocked I need to understand the whole circuit better first.

thanks

[sibainmud]

All of that stuff is for emission control. I may pay to check if the butterfly valve has been removed.
As mine was non-turbo to start with, i removed that actuator and shaft when fitting the cross-over piping.
Here's the pics on this thread.
http://www.offroadexpress.co.nz/Forums/viewtopic.php?f=18&t=25281&start=30

Cheers,

[jetskiwi]

So with the vacuum line closed off, the butterfly could have become closed in the throttle body and starved the air flow? This would match the symptoms of low power and black smoke. Perhaps the intake pipe is coked up & needs a clean.