Anyone know what this valve is on the 2.5 V6?
The in/outlet pipe arrowed is open to atmosphere at idle and shows inlet manifold vacuum.
Could it be something to do with the charcoal canister setup which is not present on my car?
TIA.

Yeah that's the purge valve. # WTV100071 I think.

Purge valve then, thanks Sidewinder.
From a bit of research it appears that it's supposed to open under specific (lean burn?) conditions under ECU control.
The car drives absolutely fine if a bit thirsty (!) but it doesn't seem right that the valve is open at idle and it seems to stay open as you raise the revs but that doesn't really replicate driving conditions.
Can't see why it would do any harm to block it off so I'll give that a shot.

Can't comment on the V6 but for what its worth the connection that previously went from the inlet manifold to the charcoal canister on my 160VVC engine (when it was still in the TF I took it from) was blanked off for the GTM install and it seems to work fine. I'm guessing the valve is supposed to open on the overrun to prevent unburnt fuel escaping to atmosphere. I would have thought that if it is open at idle it would let too much air back in and make it hard to get a slow enough idle as the idle air valve only opens a tiny amount. I suppose there might be a one way valve in the charcoal vent line though?

I'm with you Sanzo, it would seem to be just a big air leak but maybe the ECU compensates at idle?
Anyway, I'm blanking it off so we'll see what happens!

On the K engines there is a charcoal canister with integral purge valve on top, this is connected to the inlet manifold and fuel tank vent hose. Engine off the fuel vapour given off by the fuel tank is captured in the charcoal rather than being allowed to vent to atmosphere (which is non-environmentally friendly). Engine running the ECU commands* the solenoid to open the valve to allow the 'fuel' stored in the canister to be sucked out and burned in the engine. * this is done under certain conditions, but i've never found info on when exactly and under what conditions.

Your V6 system should work the same way, though it looks like your valve is separate to the actual char cannister rather than being all one module.

If air is being drawn in via the open spigot, this is bad cos it's 'dirty' air going in to the 'clean' side of the intake?

I can't think of any circumstance where it would be beneficial to have that valve open to atmosphere after the filter/throttle-body and, as you say, sucking unmetered/unfiltered air into the manifold.

Just capped it off and it starts, idles and drives absolutely fine.