09 V70 2.4D Euro 4 - Boost control issues

[foggyjames]

Hi all,

My friend has a Euro 4 2.4D on which I've been trying to resolve some issues.

Symptoms: Goes into semi- limp-home mode - reduced performance on full load (after 3-4s?), but (generally) no text display. Full performance will return after circa 5s. I had these exact symptoms on my P2 Euro 3 D5 when it had overboost issues.

Relevant codes:
ECM-P200400 - Intake manifold runner control stuck open
ECM-P200A84 - Intake manifold runner performance - bus signal / message failures - signal below allowable range

ECM-P023484 - Turbocharger overboost condition - bus signal / message failures - signal below allowable range
ECM-P023468 - Turbocharger overboost condition - algorithm based failures - event information

Possibly relevant:
CEM-U030100 - Software incompatibility with ECM/PCM
ECM-U032200 - Software incompatibility with body control module

The car had a broken swirl flap arm (https://www.volvoforums.org.uk/showthread.php?t=296940), which I replaced with a more substantial home-made replacement. This *may* have been the wrong length, but I reckoned to size it up pretty carefully. There's a chance this is a residual code while it sorts itself out, but it's a bit of a mystery as to why this is still coming up.

We were previously seeing both under- and overboost, and the car makes an audible whistle on-boost. A pressure test revealed a leak which appeared to be coming from the intercooler, which I have replaced. The noise might have reduced a little, but certainly hasn't gone away. The underboost code hasn't returned.

I am now focusing on the checksum error codes (which have been there since day one - while the boost control codes haven't, I don't think) in conjunction with the boost control codes, which now both report an overboost.

Thoughts:
1) Might we be seeing the results of a dodgy remap, given the checksum codes...? Increased boost, but protection not adjusted? It certainly pulls well until the boost is pulled back.
2) This is a Euro 4, so all sorts of complexity is introduced. Could this be an issue relating to the throttle body, EGR valve (which on some models has a bypass, I understand...?) or other nonsense I'm not used to (as, primarily, a Euro 3 dweller).
3) On a Euro 3, very few things can cause an overboost condition - only really a damaged VNT control solenoid, or stuck VNT vanes - everything else causes low boost. Any new overboost causes to be aware of on a Euro 4? My Euro 3 made some very odd noises when it was overboosting, so the "boost leak" sound might, for example, be weird induction noise.

Ring any bells to anyone?

cheers

James