I got same problem
Cleaned the ISCV today with carb cleaner, cleaned all connections and retightened all vacum hoses. Still no joy. Idling about 1500 / 2000.

However, possibly related...

1. Last week, the interior heater fan and reverse light stopped working. After some investigation it was narrowed down to a duff relay. This was changed and the heater fan, radiator fan etc worked again...

2. The rear boot popper stopped working the same time I changed the relay. The idling problem also started at this time.

Any possible relation? Is there anything electrical cthat could be affecting the idle that would be influenced by the boot popper / fan relay?