Looks like you have a JDM throttle body and intake manifold. My old B16a swap came like that.
The nipple on the top of the TB (not the one going to the charcoal canister but the other one) is for the map.
In Japan....they had the map mounted to the firewall and the vacuum line went to that nipple on the TB.
I can see where the old owner put the map on the IM. I am not sure if that matters or not. I would think it does b/c the map is usually on the throttle body which may effect how it reads at idle
A USDM B-series throttle body will have the place for the map to mount on the top of the TB.
If you look at my B16a swap thread (bottom of my signature) you can see how I mounted mine (until I got a USDM TB).
I made a bracket to mount it near the fuel filter and ran a vacuum line to the TB. I had no issues.
I hope this is your issue.
Have you checked the TPS with a multimeter? Does it have rivets holding it on or 6-point screws or phillips scews?
Depending.....this could mean its USDM or JDM or has been replaced and maybe not calibrated correctly.