We've had this car in for a few days now. Originally came in with accelerator pedal sensor fault and low boost. Pedal sensor is fixed. The car is boosting to about 5 psi and holding for a bit then going to around 15psi at about 4200rpm. We put it on the dyno and the first run saw a peak of 17psi at 4100rpm, on the next run the mid range boost dropped about 0.5-1psi, and so did the next, and the next. They all regained the same top end power and boost from 4200rpm onward though. They also all dropped the boost at 2700rpm. We replaced the MAF and MAP. If you leave the battery off to reset the ECU it regains the 17psi boost line and then starts to loose it again.
On the pic attached the boost is the dotted line. As you can see the red lines are the first run and the yellow is the 7th.
Theres no codes, no stutter or missfire, no strange smoke. BCS seems to be doing its job. No boost leaks or vac leaks. Actuator is holding positive and negative pressure. ECU seems to be pulling boost. Service light is on, no EML light. Car was remapped by REGAL at some point, only a receipt no dyno printout. Is the overboost feature faulty.

And help or thoughts would be great and thanks in advance.

vxr corsa boost problems.jpg