After 2 years and 2000 miles of drive cycles I discovered on pg 14444 of the 3000 page XK8 workshop manual, "Drive 1100-1600 RPM for 23 seconds 31-45MPH to complete the cycle for Catalytic converters." I am now ready for smog 2 days before the car was going to be sold to a Mexican buyer, and shipped to Mexico, since it wouldn't pass Ca. smog. I have spent thousands on Expert Mechanics who offered dozens of opinions, rode the freeways for hundreds of miles at 55 mph, and all I needed was to find a road where I could drive at 40mph for half a minute without getting run over!