13.9 AFR commanded

[Speedytec]

We're busy dialing in a LSJ + TVS (3.15 pulley, 60lb's, ported head with springs. balance delete, 3" MAF tube) AFR's are pretty spot on, but in the log it's sometimes commanding a 13.9 AFR during cruise. This often happens after a pull and Fuel Trims stop at those moments, but my Closed Loop flag shows enabled...
Any clues what's causing this? (Read something about AC causing a 13.9AFR, but this car has no AC fitted.)

Also we have some idle issues. TB is clean and after tweaking it's now OK-ish, but the STFT's show very little up-down movement. Is this typical for 60lb's? My own 42lb tune shows a clear saw-tooth pattern at closed loop idle.

[Area47]

rear 02 test

[Speedytec]

I thought the rear O2 test was a slightly rich period followed by a lean period? Like in this screenshot; commanded 13.4 AFR followed by a 16.4 AFR.
Car has a working rear O2 and a cat fitted. Just goes to 13.9 after some (liniter) rpm pulls...

(That WB log reading is probably off, as we use the AC input with a PID tweaked for his WB output but the custom PID's don't copy well. His WB AFR's are spot on.)