Hello! First off, I spent a while searching, but this problem seemed to be happening more with modded wrx's, barely any stock ones. Therefore, I thought a well-detailed question with pics might be beneficial not only to myself, but for future searchers too.
I just bought an 04 WRX Sedan that had an MBC on it and a Greddy catback. Nothing else seemed to have been touched. Upon reading, I found that MBC's are not a good idea for our cars due to the possibility of hitting full boost at partial throttle. Therefore, I decided to return the boost control to the stock solenoid. After reading up on the hose locations, etc, I finished removing the MBC and returning it to stock. I had to use new hoses (They appeared to be the same inner diameter as stock) since the previous owner had butchered the stock ones. I then only boosted .05 and realized the restrictor pill (orifice), was gone. I ordered a new one form Subaru and installed it today in the hose between the compressor and the "T" that splits the line to the wastegate acuator and boost solenoid (The location of the pill is shown by the yellow arrow). I used a 3/16" T fitting (pictured in red arrow), since I did not have any 1/8" fittings. The green arrow points to the only stock hose left, the one from the side of the boost solenoid to the top nipple on the intake.
From there, I put a long hose from the T to the bottom of the boost solenoid. The reducer to go from 1/4" to 1/8" was missing, so I replaced it with a 1/4" to 3/16" reducer (pictured in light blue arrow).
The other hose going into the side of the boost solenoid was stock and went to the intake nipple (pictured in green arrow). Funny thing here is that it was disconnected when I bought the car and the nipple on the intake was capped off. I removed that cap and replaced the hose onto the nipple.
After all of this, I reset the ECU and took her for a spin. The boost goes to about .09/.1 and then drops to about .06, then back up. It oscillates like this through most of the pull and then seems to settle at .05 again. As far as I can tell, everything is hooked up properly, except for the fact that they are not stock hoses. I know I am also missing the inline coupler that goes in the line from the T to the solenoid, where alot of people do the 3/16" mod. There is no inline coupler since the hose goes uninterrupted from the T to the solenoid. I doubt it's a boost leak since my boost was stable before I replaced the restrictor pill, and even when the MBC was on. The hoses look bigger than the stock hose in the picture, but the inner diameter seems to be the same. What do you guys think?