If you don't create any Layer 3 interface (Switch Virtual Interface or SVI) in your existing VLANs, they will not be affected by enabling IP routing.
So create your new_vlan in conf mode, vlan. That gives you a layer 2 vlan. Then go into conf mode, interface and create "interface vlan new_vlan" with IP address etc. You now have a SVI in the VLAN and it should be up/up.
Of course IP routing doesn't have any real function until you have at least two routed interfaces since routing is fundamentally about going from one network to another.
Hope this helps. Please rate helpful posts.