I've been wondering if part of the trouble with Elise idling is related to our continuously variable valve timing setup. The idle issue which I have noticed from time to time tends to occur after periods at moderate or more load and cruise or higher RPMs. Then when it is time to idle things can sometimes go awry. But if you turn the car off and restart it the idle is perfect. When you start the car, the cam timing is set to minimal overlap. But at the higher operating speeds and loads the intake cam is set for higher overlap which if used at idle would tend to destabilize it. Just a thought. If this is the case then it could be a simple matter of reflashing the ECU, or it could be something mechanical such as enlarging timing controller orifices. Toyota uses thinner oil in their applications of this engine. Just a thought. It would be cool to datalog the variable valve timing to see if that could be a factor or not. Usually idle woes are traced to other things in any event such as the idle air valve, base idle, plugs, etc.
In looking over the cam timing specs it appears that our small cam has about a 228 degree duration with 7.25 / 7.25 mm lift. The cam phasing can be varied over a 43 degree range. The large cam lobes have 292 degrees duration and 11.4 / 10.0 mm lift.