This is a very common problem with eBay turbos. Since the wastegate port is so small, excess exhaust gasses are forced through the turbine wheel and raise the boost higher than intended. This is called “boost creep.” This can also be a problem if you’re trying to run a very low boost level, say 5psi, but have a free-flowing exhaust system (2.5″ – 3.0″). Opening up the wastegate port in the turbine housing will allow more exhaust to flow around the turbine when desired.
-I did not remove very much material in this video, check out a much more aggressive version of this procedure on one of my favorite YouTube channels: Tom’s Turbo Garage – DIY Turbo Porting