You can check the strength of your vacuum by unplugging one of the hoses and checking for suction. If it's okay when cold, I doubt it's a simple vacuum issue.

Since your IACV and knock sensor are surplus, I'd look there. Though a knock sensor problem would result in running issues rather than idle.

Most likely the surplus IACV is just not up to snuff. Idle issues often start there.

I'd also check the PCV system, just in case, to see if there's an issue there. That one can also cause issues when hot.

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You're correct that the Cam Position Sensor issue results simply in stalling. And yes, the non-RS Lynxes do not have O2 sensors. Since our OBD ports are weird (neither OBDI nor II), you'd need to go to a specialist with the right connector to diagnose. Check up on FCP for places that have it. AFAIK, PowerTorq and Speedlab both have the right connector, but if they're too far away from you, best ask around where else this can be done.

Impressed that you've ticked off all the boxes on what's not wrong. ;) I'm also tracking a running issue with my Number Two Lynx, and I've got vacuum lines plugged with old spark plugs and fuel return lines (oh, by the way, check the Fuel Return valve... see if the running changes when you disconnect the electrical supply to the actuator) clamed with vise grips and I'm still stumped... Hahaha... might have to pull the fuel pump to check the filter soon.