If your on or off the throttle its common to see a lean or rich condition , its steady part throttle or WOT that you need to check the AF gauge
A stumble at idle is a good indication of a lean/rich condition which could also be there at steady part throttle driving but the closed loop is correcting it ( can correct up to +/- 25% ), this could be an issues when shifting and always trying to correct the closed loop , In most cases if your off in closed loop ( idle and part throttle fueling ) it changes the open loop fuel ( wot ) fuel as well , your WOT fuel should be in the 12.8 range , whats your WOT A/F ?
Tom