AFR bouncing around. Normal?

I have an AEM fuel gauge. Simple question: why does it constantly bump up and down when I am cruising. Pretty much in a rhythm it will go from ~13.8 to ~15.3....bounce up, bounce down, bounce up, bounce down about once a second or faster. Never sits at stoichiometric for even a blink.

Now, when I go WOT it quickly drops to 11-11.2 and stays there. Just wondering if this is normal behavior. Thanks.

It's not supposed to sit at stoichiometric. It's supposed to oscillate. It cycles rich to supply gases for the reduction catalyst (NOx) and lean to supply gases for the oxidation catalyst (HC, CO). In fact, if it didn't oscillate it would throw a code.

That's why forums like this are so helpful. Thanks so much for the simple and clear explanation.

Also, you can see it in a data logger with the "AF Correction #3" and "Closed loop target AFR" parameters.