I have looked everywhere for people with similar symptoms and can't seem to find any. I have a 2006 legacy gt with AVO drop in filter and TMIC, sti UP, Cobb DP with cat, borla CBE an its tuned by infamous1.
I noticed awhile back that I was getting a turbo whine that I kinda just assumed was normal. After gettin the car tuned it ran fantastic. About 2-3 months ago I started loosing boost until my car had been ran for a long time (8-10psi). I made me a brilliantly engineered boos leak tester with an empty cup holder style container of dash wipes, a valve stem and transfer case rear output shaft seal for a Nissan Titan.
I plugged the exhaust an pumped the system with smoke on a evap leak smoke machine. I found one heck of an UP leak so I replaced that gasket and fixed that. Now I still lose boost but not as often or for as long. I never build boost until my thermostat is fully warm and now someone's it only hits 8-10psi until its been driven a little longer than it being warmed up and before it was almost all the time. Now when it does act up sometimes it will kick in full boost on a test pull to see of its working but it will spike 8-10 and hold until its higher rpm then shoots to 16-17psi and then will be perfectly normal until I shut the car off and let it cool down again.
I have checked for boost leaks doing the smoke thing but if I try to pressurize it more than 4psi there is a valve that makes a noise so I can't hear any leaks over it and I was told that valve is supposed to do that. I was thinking it may be my oem bcs but the fact that its electronic it would either work or not work, no in between but it's also solenoid still and had mechanical moving parts so I don't know. I'm kinda at a loss at the moment.
If anyone has seen this before or has some useful tips please help.