XF EFI Won't Rev - Sometimes
Every so often when I give the XF some boot, a scary sounding rattle and vibration comes from up engine ways, and it doesn't want to rev out as quickly or nearly as smoothly as normal.
It seems to be quite random - some days it does it, some it doesn't. Temperature, fuel, how long it's been running for, nothing seems to have any effect on whether it does it or not. The only thing that is the same is that it happens under acceleration in any gear over 3000rpm.
The engine has been rebuilt with some go fast bits, but that was well over a year ago. This has only happened in the last couple of months.