Sorry, probably something really easy, but what is this I am pointing to in the picture on top of the last coil pack?

Looked through Haynes manual and cant seem to find it....

It's the vacuum reservoir.

Certain things (like the N249 and N112) need a vacuum to operate at times when the inlet manifold might not have a vacuum, so it accumulates a vacuum from the inlet manifold in that reservoir and they use it when they need to.

If you remove your N249 and secondary air system its redundant.

It's the vacuum reservoir.

Certain things (like the N249 and N112) need a vacuum to operate at times when the inlet manifold might not have a vacuum, so it accumulates a vacuum from the inlet manifold in that reservoir and they use it when they need to.

If you remove your N249 and secondary air system its redundant.

Cheers fella, I have been thinking about removing the said above bits anyway as seems an awful lot of extra vacuum piping. more to go wrong. Had similar issue with Plenum on the 300ZX ended up bypassing them, problem solved.