Always considered the B16A manifold to be better suited to street and daily driving. The longer runners and slightly smaller plenum gives for a more usable power band mid range. Just results in a bit of a lazy top end above 7k compared to the Type R B16B/B18C manifold.
Idle shouldn't be affected at all. Will more likely be fault with the Idle Air Control Valve on the back of the manifold just to the right of the Throttle body. Try cleaning it out and then doing an ECU reset. Might be worth checking the Ign Timing as well while at it. Found when I had fitted my dizzy a little off it raised my idle a bit as well.