what is this?? (pic of engine bay)

[doh boy]

what is this? (circled in red)

[mandoz85]

That is Your AIV, it is smog related.

[LanceS13]

That's the AIV system. It's an emissions device that diverts clean intake air to the exhaust to burn off any un-combusted hydrocarbons ::I think that's how it works::.
It can be removed w/o affecting performance (probably affects emissions) or throwing a code, at least on S13s. Just be sure to cap off the manifold bung.

[doh boy]

thanks for the quick replies!