New to tuning but figure I would give it a stab at it.
I have a B18C5 with JRSC. Professionally tuned January but I have a small part throttle cruise stumble and AFR sweep that gets on my nerves.
As far as the Stumble, from my research and what I can tell from my datalogs, I have a close loop issue.
Problem appears during cruise, around 8% throttle and 4k RPM, Short fuel term trim usually sweeps from -3% to -16% then goes flat at 0% for a second which then the TPS flatlines causing the Injectors to cut out which is the stumble. Everything picks back up after that for another minute or so.

Second issue: Air to Fuel sweeps from 13.3 to 16.8 within seconds. Enough to make you feel seasick. ha

Any initial Ideas?

 

You focus more on the AFR change in your description instead of the stumble. So by going off the information given - it is perfectly normal for the AFR to read lean upon closing the throttle plate with deceleration. Are you trying to say you have a stumble while driving or problems with tip-in after closing the throttle plate and reopening it? OR do you mean everything is flatlining without you changing throttle position while cruising?

 

Sorry for the confusion. Two different problems. Afr sweep is at light throttle. I figure the rate of change should be less drastic..

The stumble is from the flatline without changing throttle position. Usually at parking lot speed or at cruise. I can see it in the datalogs, short term fuel trim goes and stays at +1% then tps flatlines causing injectors to cut out. All of this at cruise, 80mph around 8% throttle & 4k rpm.

 

This is some photos I have of the stumble at cruise.
First the noticeable symptom. Fuel cut from tps flatlining but is at cruise so throttle should stay around 8%.
So I thought TPS or wiring but then I looked at Closed Loop (second photo)
Short term fuel trim levels out at 0% before the TPS flatlines.
I checked all the calibrations for closed loop and it all matches what Hondata recommends.
Hope this clears up any confusion.

 

Looking at the second chart. It appears the problem is caused from the bad O2 sensor or a short term fuel trim issue.
What does it look like?
BTW- From what I can tell my AEM wideband gauge never stops sweeping until the fuel cut.