P0234/p0236
 

My '02 XC70 140K mi is showing the following codes. I can reset them but eventually they come back,

P0234/ECM-6805 = Turbocharger (TC) control valve, boost pressure fault. Pressure too high
P0236/ECM-170F = Atmospheric pressure sensor / boost pressure sensor range check. Faulty signal. Intermittent fault

Additionally, the engine is not happy with whatever is wrong. It idles okay but occasionally seems to get a hiccup causing a large amount of vibration and almost a stall, which it has done once. The random vibration thing has been common on my engine for a while, the stalling and codes are new so I guess it's a developing problem.

The boost pressure control valve makes an audible clicking sound, presumably as the solenoid switches on and off, although I don't know if that indicates normal function or not. Replace? I checked the MAP connections but they seem fine. The fact that I can reset the P0236 code without it immediately reappearing suggests that the MAP sensor itself isn't bad, could it be the boost control valve? Any other ideas, diagnostic tests I should try?