Weird O2 reading?

[cwelk87gn]

How much fluctuation is normal for o2 counts on the Scanmaster? When my car idles, it may register 325 then shoot up to 550 then 200.... you see what I mean. It never remains at any constant level and like I said may change a couple hundred counts in any given minute, is that normal? I recently replaced the AC delco unit with a Denso and it still does the same thing.

 

[bruce]

In closed loop at idle they're supposed to dance around.
The ecm is only trying to AVERAGE a 14.7 AFR at idle, and it runs rich and lean of that. The richness and leaness is necessary for keeping the converter happy.