P0234 with replaced TCV & MAP Sensors - 2001V70 2.4T

[Harleyvh]

Here is the situation.... long story with as much detail as I can give you

2001 V70 2.4T with 253.000 km.
Autotech Tune
IPD HD TCV MK2 / MAF (BOSCH) / silicone vac lines changed this summer.

The car had a situation of "over boost in acceleration" when the temperature is lowered into the -10/-20 ....
even hit the "limp mode" on one occasion.

Actions taken to diagnose:
* I deleted the codes
* I removed the tune of autotech (to-22C ... fun, fun, fun) ... car still had an erratic boost
* Generated codes: P0234 / P1238 / Check Engine Light
* I replaced IPD TCV wih new OEM TCV and I erased the codes.
* Same codes returned: (P0234 / P1238 / Check Engine Ligth).
Codes are present when the engine runs but are not seen by my scanner when stopped

Behavior during acceleration (with the new OEM TCV / no tune)
* Heavy Load => car goes 8-10 PSI (and even hit my indicator 15) for a short time.
* Normal Load => car up to 5 PSI boost and loses. I am able to get to 5 psi for a short time then PSI falls to 0. The car continues to accelerate but very poorly - no boost.
To get a boost again, I have to release the accelerator and re-apply.

From VADIS :
P0234 = ECM-6805 Turbocharger (TC) control valve. Pressure too high. Permanent/Intermittent fault, B5244T3
Diagnostic trouble code (DTC) information
Condition
If engine speed (RPM) is above 3500 rpm and the engine is operating at a
high load, and if the boost pressure (from the boost pressure sensor)
is higher than a designated value, which at maximum boost pressure is
approximately 20 kPa (2.90 psi) above normal boost pressure, this is
interpreted as a fault and diagnostic trouble code (DTC) ECM-6805 is
stored.
Substitute value
reduced boost pressure
Possible source
* hoses between turbocharger (TC) and turbocharger (TC) control valve
respectively turbocharger (TC) control valve and pressure servo are
loose or are blocked/damaged
* faulty turbocharger (TC) control valve
* faulty boost pressure control (BPC) valve pressure servo
* sticking boost pressure control (BPC) valve
Fault symptom
none
P1238 = ECM-6806 Turbocharger (TC) control system flow fault. Flow too high. Permanent/Intermittent fault, B5244T3
Diagnostic trouble code (DTC) information
Condition
If engine speed (RPM) is above 3500 rpm and the engine is operating at a
high load, the control signal to the turbocharger (TC) control valve is
at maximum and the boost pressure (from boost pressure sensor) is lower
than a designated value (approximately 20 kPa (2.90 psi) under normal
boost pressure - signal too low).
If the air mass (from mass air flow (MAF) sensor) is higher than a
desired value (signal too high) it is interpreted as a fault and
diagnostic trouble code (DTC) ECM-6806 is stored.
Substitute value
reduced boost pressure
Possible source
Signal too high:
air leakage after turbocharger (TC)
Signal too low:
hoses between turbocharger (TC) and turbocharger (TC) control valve
respectively turbocharger (TC) control valve and pressure servo are
loose or are blocked/damaged
faulty turbocharger (TC) control valve
faulty boost pressure control (BPC) valve pressure servo
sticking boost pressure control (BPC) valve
Fault symptom
Warning lights and chimes/Malfunction Indicator Light ("Check engine" light) indication/no indication
Driving/Poor performance/lacks power
Driving/Hesitates/surges/Unsure when/at all times

The above VADIS code explanations seem to point to a faulty MAP sensor (never changed it before)
So I changed the MAP sensor and i retested the car
(even followed the new TCV set-up routine)

Results: same behavior only one code present: P0234
I have to be gentle on the accelerator to eliminate the possibility of overboost.

next steps:... I'm thinking about the following: check the lines....
* Re-check the vaccuum lines
* inspect the intake pipe (from MAF to turbo)
* inspect Turbo - Intercooler pipe & intercooler to Intake manifold pipe

and if all lines are ok the explanations above points to the BPC Valve:
"faulty boost pressure control (BPC) valve pressure servo / * sticking boost pressure control (BPC) valve"

Questions:
* Am I missing something here?
* Where is a Boost Pressure control Valve on a V70 2.4T?
* Any other suggestions?



Thanks in advance.