Before looking into modifying the subaru, I wanted to know the reliablility of a tune (OpenSource) in winter months if I plan to get the car tuned in the spring/summer time.
Your tune is only going to be as Good as your tuner. Pick a good tuner and winter will have little to no effect. Pick the wrong one and it will start hard and idle poorly
Like jason said, all depends on the tuner. There are parameters in the ecu that need to be set correctly to adapt to changing ambient temps. Same goes for when it is really hot out. My tune from Nuke starts and idles like stock even when it was -20 degrees. One thing that MIGHT not be able to be tuned out is boost creep when it is super cold if you are catless and have an internally gated turbo just because the air is so dense and the internal wastegate is only so big. Even if you get boost creep that can't be tuned out you can always go with an external wastegate.
