Vitara AllGrip sorry tale

[AndyBUK]

So here’s my tale of woe, I’d be grateful for any thoughts. I own a Suzuki Vitara 1.6 diesel AllGrip, 10 years old and with 92,000 miles on the clock. I’ve owned it since when I bought it in Sept 2022 with 80k miles run. It came with a good service record. It’s never given me any problems apart from a very occasional oxygen sensor alert. As it’s now 10 years old I decided to get the cambelt replaced for peace of mind, and at the same time had a service with filters, oil, etc.
I got the car back and drove it home (6 miles) with no performance issues. The next day I ferried some furniture for my daughter in my tiny 4ft x 4ft camping trailer. On my way home, with an empty trailer, I accelerated mildly up a hill and immediately got a check engine and limp mode. The code was P0238 – turbo overboost.– never had this before. At this point I’d maybe done 40 miles since the service.
I took it back to the garage – they did a quick check of their work and found nothing. The code recurred as I drove home. I took it back again and the MAP sensor & Oxygen sensor were replaced. Same code as I drove home, plus now the O2 sensor was showing biased/stuck lean as well.
Got it back to the garage again, they suspected an intercooler or hose, so they took the front off the car, removed and cleaned the intercooler & hoses, checked the timing, and again found nothing.
As I drove home I got a DPF warning! I had a slight suspicion that the new oil level was on the high side, so I syringed out 0.5l to get the reading in the middle of the dipstick band. I then drove the car at 2,500 -3,000 revs for about half an hour and cleared the DPF warning.
The biased/lean code has not recurred, neither has the DPF warning, but I’m back to P0238 again.
Today I gave the engine a “Revive” chemical clean, but P0238 was back on again after my test drive.
Any suggestions gratefully considered.

Cheers, Andy