A4 B6 TDI 130, Limp Mode after hard accel

[RichardOfReading]

Advice would be welcomed. One of the first B6's, have owned from new. Driven gently / normally, runs fine. Something like a 4th gear overtaking manouevre will trip it into limp mode. Stopping and restarting the engine resets it OK. Could this be the engine control system wrongly detecting an overboost, eg, a boost sensor which has lost its calibration ? (After 20 years, so might I).   

[Steve Q]

I recommend a diagnostic check to see what fault codes flag up. Could definitely be a sensor.