Hi Jon, congrats on the XJS. I also have an '88 and like it better than the newer one we have. By your description I would start looking for some vacuum leaks. I say this because on a speed density system like these cars have, a large vacuum leak will cause the ecu to think there is low vacuum, hence heavy load condition. It will then dump fuel. That could be why your cat was glowing red. Or perhaps you have an early Marelli system and are in the middle of having a Marelli meltdown. Check for the XJS help book by Kirby Palm. I will explain what to do if you have the Marelli. I have found the V12 to be quite gratifying to work with. Not necessarily easy but definitely responsive to maintenance. I had many things to straighten out on our Lucas system, even though it seemed to run fine at the time. Much better now though!