Ok, I've done the following:
replaced cap, rotor, wires, spark plugs, thermostat, coolant.

Surging idle is still there!

The last thing to check would be the IACV?

I've read online that IACV is all about cold idle though, not once the car is warmed up. So what's up with that?

The car idles fine when cold, once it's warmed up it starts surging, and at each surge the exhaust kind of... farts.