Lean idle. Rich cruise.

PS. Even when cruising, when there is a slight downhill and we lighten up on the throttle, a high vacuum is created under the mostly closed throttles and guess what happens.



There's less air mass coming through and more vacuum at the idle port and transition slot so the 'idle circuit' starts supplying fuel again.
I've posted some data tables showing that if your interested.

The better we can get the idle circuit to work at idle, the closer we can get the idle vacuum to where the idle system will choke. Choke in this sense is the pressure difference where increasing pressure no longer pushes more fuel through.