AU-not passed

Hello.
after which my car, a 93 4.2 V8 always had excellent values at the AU, I failed completely this time. I've been driving with gas since October last year, lambda probe and spark plugs are new (according to Frank Ziehm it's also the right candles) and I use a K&N air filter that I washed out before about 4500KM. The car has been driving exclusively in the city since last summer, whereby I largely avoid STop And Go traffic. The electrodes of the candles are gray, I suppose he's running too thin. However, the CO content has been well above average. Do you have any idea what this could be?? Original LuFi in and burn the engine out? I cleaned LLRV with the most precision, but the CO content is far too high at all speeds. According to the computer, Lamda probe works perfectly. The guy there says it's not really the Kat's. We tried it in both pipes, a piece in front of the pipe. But still no chance!
Maybe you know some advice. Thank you!
MfG Martin