Okay, I've done exactly the above and got myself VDASH and a cable. Reset all the stored codes from previous abuse and went for a drive. Sure enough the "Reduced Engine Performance" warning comes on after about 10mins of driving and usually after a pull when the BOV vents.
Codes are:
ECM-9100: Clutch pedal switch. Faulty Signal. ECM detects an internal fault or a fault in the throttle motor circuit in the throttle unit when the ignition is turned on.
ECM-640C: Turbocharger control system. Signal too high. The ratio between the measured boost pressure (measured value from the boost pressure sensor upstream of the throttle) is incorrect. A DTC can be diagnosed when the engine is running and the turbocharger control system is not active.
ECM-21AD: Long-term fuel trim load, bank 1. Lower limit. The ECM receives fuel/air mixture information at the upper and lower part load ranges from the heated oxygen sensor. If the fuel air mixture deviates from ?=1, the short term fuel trim compensates by adjusting the injection timing to achieve ?=1. When the short term fuel trim makes an adjustment, the median integrator must be adjusted by the long term trim. A DTC is stored when the long term trim must be adjusted to near maximum in the upper and lower part load range. The DTC can be diagnosed when driving under specific driving conditions.
It all seems to point towards not liking the fuel/air ratio after the BOV vents to atmosphere. Might have to return to stock to solve this one. Any further clues?
