the idle on my 4 gsr is a bit funny! when it starts from cold it only ticks over at about 800rpm! too low I think, then after a run it sometimes insists on 1500rpm but other times its spot on 1000! I don't suppose I have an idle reset? perhaps I have other problems, like my de cat or vent to atmos forge dump valve?!
Have you tried an idle reset? Idle issues won't be decat or bov. A vta bov may cause stalling issues when stopping but not often cause idle issues as you describe.
not sure how to do an idle reset on my iv ! im totally new to evo ownership! also is the motor in my 4 supposed to make a funny whirring noise when you rev, almost like a small quite supercharger? no belts are rubbing or anything, from inside the car you cant hear it......