So I’ve been on a wild goose chase for quite some time with a rear o2 (b2, s2 to be specific) acting up and throwing CELs.
Here are the faults that I see. The post-cat o2 reports that it’s too rich, meanwhile at the exact same time the pre-cat o2 reports that it’s too lean!
Further in that thread I actually went on several mid-range drives and logged data using VCDS and believe I caught the rear o2 acting “lazy” once I got back on the throttle after coasting for several hundred feet. Graph seen here. It is interesting that when this happens, both the long term fuel trim at idle and long term fuel trim partial values both go to 0% for bank 2. I suspect that in certain cases when the rear o2s aren’t functioning correctly it causes the ECU(s) to ignore those fuel trim values all together. I don’t notice any bucking like you describe, but I could very well be leaving some HP on the table. Thankfully I don’t drive it all that much since I’m fortunate to work from home otherwise I would be very concerned daily driving it.
I could be WAY off the mark here. This is literally just a hobby of mine. I’m again due for PA state inspection soon and told my guy @ German Automotive Specialists in Plymouth Meeting that I’m going to throw some cash for labor at it for them to really dig in a diagnose what is going on. I’ll be sure to update everyone once I have more info from them.