idle control valve ?

could be your o2 sensor, AFM or maybe you have a leak on one of the intercooler hoses, just throwing some randoms here, but sounds like an intake problem

If you were sucking in water (trust me mine was doing it) it would get to about peak boost, 4 thousand on my VF34 so about the same on your VF35, and it would jerk violentley. Almost like hitting boost cut or a 'Brick Wall'.

02 sensors would make your car surge during times of hot and cold. Again, i had this problem and when it was cold, it would drive and kind of stutter, it eventuated to when it was hot aswel. Again, doesnt sound like what you are getting. Not being able to idle properly could be ICV (Idle Control Valve).

If it happens when its only rainy, you have pretty much figured out, its a water issue. Sounds weird ;p

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Remove pod filter and replace with OE airbox...

If this is supposed to mean your engine will not rev higher than 3500 RPM while driving - Conclusion - you have a contaminated Air Flow Meter. Your STi will also not make boost whilst in "Fail Safe" mode with a stuffed AFM either.

Your going to have to replace that Pod Filter with the factory airbox as it appears your AFM is getting contaminated either due to inadequate filtering and/or moisture contamination when it rains.

You are far better putting back the factory airbox back in (minus the resonator - snorkel), fitting a silicon airbox to turbo intake pipe and then getting a reflash tune from the Verso boys.

Ps. Air Flow Meters can be cleaned with a spray can of CRC Contact Cleaner.

J

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