jon-

What tyre did you fit? I ended up with a set of AllSeasonContacts, you can see them tested here https://www.tyrereviews.com/Article/2020-Tyre-Reviews-All-Season-Tyre-Test.htm in 18" on my vrs and was happy with them, even if the steering was a little wooly

It's titled turbo pressure control in the app so I was guessing maybe something to do with the waste gate control

I agree with your theory but bottom left is boost pressure isn't it? I'm still not really sure what bottom right is

I don't think this turbo has variable geometry, and a blocked cat is a good idea but it wouldn't end up flowing ok at the end of the RPM. My money is on wastegate. Maybe.

The car had been run on 95 but it was on a second tank of vpower. Fuel alone wouldn't cause that massive drop in power / torque at 3500rpm

Nope, car has definitely never been remapped, my dad owned it from new!

No codes at all! I'll go out and check fuel trims, I'm not sure I can see knock in my app. I just threw new plugs in and I changed a coil pack that had melted to the Head but no change at all. It's coming on boost so strong, it shouldn't be that much torque that low down.

I just noticed, over 400 nm of torque, and I am 100% sure this car isn't mapped. No wonder it feels punchy at low RPM.

I recently posted about a flat spot at 3500 rpm. As it's gotten worse, I did what any idiot would do, I went to dyno it for a laugh. The healthy looking curve in the dyno plot is not my car. The unhealthy one is. I did some data logging too, and everything looks fine from the cars point of view, until it gets to 3500 rpm then it dumps all the fuel it can and pulls timing, but it doesn't pull back on the throttle. I might be wrong, but the car seems quite torquey pre 3500 rpm so perhaps a stuck wastegate? Are these electronic ones? The previous owner spent the first 48,000 miles mostly off boost.