and it wont damage the cat. the PCM is correcting the hardwritten tables by removing fuel (it will go to 44% change after it hits the 22% "wall" for long enough) to keep the mixture at stoiciometric.

keep in mind that the TPC/MAP(and baro)/MAF and O2 are "trusted" sensors, so the pcm ASSuMEs they are correct even when they may be skewed by age/contamination.

the O2 is the primary datapoint for trims....so make sure its good.