Post-mortem:

The Volvo dealer figured this one out:

It was a multi-component failure in the EVAP system (sucks up fuel fumes from the fuel tank, so they don't pollute the atmosphere.)

These two solenoid valves were both failing to actuate:

30670448 Turbo Boost Pressure valve

8653908 EVAP Vapor Canister Purge Valve

When I got the car back, all the reported problems seem to be fixed. There engine shutoff "kick" is gone, and the idle RPMS is steady at 650-700.

They used the individual solenoid valve testing feature in VIDA to figure this out, where you actuate one valve at a time, and listen for the audible click. Chalk up a big win for VIDA. The Volvo shop was happy I did some prelim stethoscope work, and heard the anomaly coming from the EVAP system ( there was a constant rhythmic valve "chirp" heard when I place a cellphone mic in the fuel filler throat).

So thanks for the advice to probe for vacuum leak with stethoscope.