I am using PTE 1200s on 91 octane and am having a bit of trouble getting the scaling / latency correct. I originally set my scaling and latency to:

1044

3.312
2.184
2.088
1.296
0.792
0.72
0.48

With the above settings the car barely ran. The plugs were black. I changed the settings to :

1044

3.192
2.208
1.512
1.056
0.696
0.504
0.288

And it idles and appears to be better, but still off. After idling ~13 minutes, AFRs are ~13.4, the O2 Feeback Trim (STFT) ~ - 5 to -10, and Fuel Trim Low ~ -12.45. The STFT was -25 but improved to ~ - 5 which I am guessing was a result of fouled spark plugs.

Any advice on : (1) why would the STFT be -25 , (2) is -5 bad, what should I do to improve, and (3) should I take the plugs out and clean them (if so with what) ?

THANKS IN ADVANCE!