BMW 2.8 straight 6 petrol.
Runs fine when cold.
After about 10-15 minutes it starts spluttering about 2,500rpm and then will not rev and hold steady at 2,500rpm or higher.
This is recorded with the camera held under the bonnet while the car initially idles and then tries to rev to 2,500rpm
https://youtu.be/iNnSF_lukwY