Did you get the problem resolved?
This is happening to my stock 1999 wrx sti version 5. I have changed the air filter, cleaned the throttle body and iacv unit. Still no change. Just changed the fuel filter and still no change. This only happens when the car is warm and the idle hunts for a few seconds before stabilising. No problems at all other rev ranges.
This has got me stumped and would appreciate any advice on this.
Also, any recommendations on who the best person in Perth that maybe able to help. Not sure if I would like to take it to a dealer but perhaps a subaru specialist instead?