Originally Posted by Morflavo

Update for everyone following this thread:
Found the problem!
The passenger (right hand) side diverter valve had a torn diaphragm. Replaced with a GFB T9488 Blowoff valve and while "low" boost hasn't completely vanished (it got worse the last few days, I fear I broke the other one a bit romping on it during testing), and boost is up from 5psi to 10ish! Photo attached.


Torn diverter diaphragm

I was able to get to it after work by removing the intercooler reservoir with the steps below:

1. Remove engine cover, passenger side intake tube via clips
2. Use E10 socket to undo one bolt on the turbocharger, unclip MAP sensor in the airbox, and lift out the filter housing and turbo elbow tube.
3. Undo the three plastic clips on the front plastic air dam that holds the three holes for intake and ECU cooling and lift it out, being sure to pull the cable out of the three channels molded into the back.
4. Remove the cap and use a siphon or fluid transfer pump to evacuate as much coolant from the reservoir as possible (easiest at this stage)
5. Undo the 2 E10 bolts holding the reservoir to the valve cover, and the T25 down in the bottom right corner. If you have a magnetic snake, this T25 will come out easy using that. I did this whole job with the car on the ground, so I had to make sure I didnt drop tools or bolts into the engine bay, never to be seen again.
6. There is another T25 screw on the top of the boost solenoid. Remove that screw, the electrical connector, and the vacuum lines. This should enable you to lift it out WITHOUT completely undoing the bottom T25 that holds the solenoid in.
7. Beneath the solenoid at the bottom of the reservoir, there is ANOTHER T25 screw holding a hose bracket to the reservoir. Remove this as well.
8. There are now many electrical connector clips holding wires to the reservoir. Undo all that you can find.
9. The only thing holding the reservoir in now is the hoses! Unclip the top hose, lift up, and undo the bottom hose. Coolant WILL spill out here, but not a crazy amount.
10. Use various arrays of extensions and a magnet snake to get a 5mm allen socket into the three bolts and you can remove the diverter valve and undo the electrical connector.
11. From here, it's the reverse order, being sure to put the new solenoid in using the correct orientation. IT IS NOT AN EQUILATERAL TRIANGLE AND ONLY GOES IN ONE WAY. I used a bore scope to fasten the top bolt and check if the others were lined up.

The left hand side (driver's in my case) is MUCH easier to do. When you do this, let the car cool off for an hour or so first with the hood open. A lot of heat builds up down there and a gloved hand wont be able to feel around to make this happen.

Originally Posted by DubVBenz

That's awesome. Since you have to remove one MAP Sensor to get it done, I'm guessing I may as well replace both MAP sensors & driver & passenger side diverter valves at the same time?