Suggest that you run with the green top sensor then, as that one is more reliable and should give you a good base to work with. Even if you're getting a good A/F ratio with the old sensor now, I'd still be tempted to stick with the green and look for other causes for the mixture variation. If the old ones dies, you'll have to switch to the green anyway.
Are you running with with everything else the same as before except for the fuel?
I had blue or black to begin with, can't remember which, and it started giving intermittent errors. Ordered a new one. Got a green one but I think it had the wrong connector. Went to my local dealer and managed to get a green one with the right connector after doing a look-up on the system. At least I think that's how it went. Bit difficult to remember now. Anyway, I've now got a green one in my AGU engine and have not had a problem since then.
In the beginning my car had a black sensor, p/n 078 919 501C, round connector.
I ordered a new one from the UK and got a green one 059 919 501A with a square connector.
Went to my local dealer and did a look-up on their system for the black sensor. Against my original number they had a listing saying that the part had been replaced by a newer part. Managed to get that newer sensor from them and it came with the round connector. The new sensor in my car now is light green, the square top sensor that came from the UK is dark green.
Going back to your original question, I'd suggest monitoring the car from cold and take it for a 20-30 minute drive logging block 003 the whole time. Afterwards review the log and see if the temperature values being recorded are stable or are fluctuating wildly. In addition, monitor your A/F ratio at the same time so you can see if that is behaving or not.
Malky, would be interested to see what that MAF flow looks like after you fit the cat. Here's a graph of some logs I did about 2 weeks ago. I've got the full Milltek, an AMD chip, an AMD DV (Turbo Dynamics), Forge SMIC and the Forge/Samco TIH. Readings at 30 deg C ambient temp. Max readings very similar to yours (K03 maxed out at about 15-16 psi, injector timing maxed out) but quicker spool which I assume is the DP/cat and the TIH.
Malta, I think you need to plot the temp data on a graph to see if it is fluctuating wildly rather than just looking at values at one point. The most common fault seems to be intermittent values. Send me the log files if you want me to plot the stuff for you later.
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