Passat TDi 2006 limp mode, flashing glow plug light?

[b6evo]

Happened twice now.

Drives fine around town, pulls hard through the gears, no whine from the turbo, no sounds of any boost leaks, no signs of any split hoses.

BKD 140BHP lump, done 175,000 with full history, 2 owner car, thousands spent.

I was going to join the motorway last week, come off the roudabout onto the slip road, got upto about 60mph not sure what gear but quiet high revs and the car lurched forward, the beep beep beep on the dash, glowplug light flashing, engine fault contact workshop on the display, then i lost power, once it dropped below 2000 revs it wouldnt go over them again.

Pulled onto the hard shoulder, got a mini autel handheld scanner out plugged that in, error code P0234 I think it was overboost? Wiped the code car drove fine as normal for another week.

Then today playing silly buggers on a dual carriageway with someone, took it through the gears, again high revs and same thing happens, lurch glow plug light flashing, engine fault etc

Just cant understand why its doing it, it appears to have had a new turbo, it doesnt whine at all and i cant see it being the original on 175k

Any other ideas?

Thanks