I recently replaced most of my turbo hoses and the small "delay valve" ( the red and gray valve sitting atop the valve cover on the B230FT). The car runs great. Boost is where it should be, no hesitation or stumbling, ... steady idle.
Decent gas mileage...just over 20.

One annoying turbo problem remains. I'm getting a high-pitched whine from the "check valve" (aka CBV valve I believe). This is the large valve sitting between the AMM and the radiator with several vacuum hoses flowing to and fro. The valve has an adjusting nut and bolt on top, right in the center of the device. If you tighten the bolt, the high-pitched whine increases in pitch. If you loosen the bolt, the whine gets lower in pitch. I suspect there is a diaghram inside that device and I suspect that diaghram is leaking, which is causing the whine.

Do you guys know what that valve does? If the whine indicates a leak, should and can it be repaired or replaced? Is there a "rebuild kit" available? I believe Bosch makes a replacement part that performs the same function, but uses a different design. I've heard the Volvo replacement part is very pricey.

Thoughts and tips would be appreciated.

PS, thanks to Steve and others who recently informed me how to replace my FPR.
New one was $15... FCP Groton. Works great.