My 1995 XJR has had the rear cats removed, and largely runs fine without them - but sometimes runs pretty rough / misfires until I disconnect the lambda sensor plugs, when it runs fine again. The sensors are new (replaced by previous owner), and everything else seems fine......... has anyone come across this kind of thing before? I searched for anything similar already posted, but haven't found anything.

 

The sensors could still be faulty, If you have a local scrap yard you may be able to try an another one for little cost.