My brothers Rb30ET is doing the Exact same thing, and he has no BOV, hopefully the Fix is the same. Few things we have tried on his RB30
Fuel pump replaced, fuel reg replaced, pressures tested to rail.
Crank Angle Sensor replaced, Leads Replaced. Spark from coil but havnt replaced as yet. (dont know if its related but could be).
and we are looking for a spare AFM to test with. But issue remains with or without AFM.
Doesnt matter what boost we run, same issue, also we noticed it only happens when it comes onto boost (while cold) but when it heats up, does it earlier, and we have checked everywhere and found no intake leaks.
Hopefully someone can Shed some more light on the subject.