Perfectly normal for super lean A/Fs upon deceleration. My wideband reads from 10.0:1 to 20.0:1. After 20.0:1 it simply reads "lean", which is displayed everytime I lift completely off the throttle.
Ken
From what I've learned in my various readings (and problems with TPS adjustments), when lifting off the throttle totally (as sensed by the TPS) and vehicle speed is "overrunning" the engine (as sensed by the ECU that Engine RPM is significantly above idle RPM with no throttle applied), the ECU does a "fuel cut" where the injectors are not opening at all, until the engine gets down to just above idle speed...
This transition from no fuel being injected to fuel being injected requires the TPS to be precisely adjusted to the factory settings (critically so on manual transmission vehicles), otherwise there is a "jerk" as you move the throttle slightly above and below the TPS idle switch closure as the engine goes from no fuel to fuel being injected...
If the TPS idle switch is set too high (switch closing prematurely while the TB butterfly is still open enough to allow significant air flow), the jerking can be very pronouced and annoying.
The closed throttle, engine overrun is a very dirty situation with regard to emissions, if fuel is flowing in the engine.. and with catalytic converters, this can't be allowed to happen.. otherwise you overheat the converter and have other problems.
In the old days with carburetors, this was the PIA scenario that required air injection pumps (in the exhaust stream) or, excessive amount of EGR injection, dashpot dampers, or vaccuum actuators on the butterfly to hold it off the fully closed position, and other Rube Goldberg fixes... When it wasn't perfect, you had popping from unburned gas dumped in the exhaust flashing off and, of course the possibility of overheating the catalytic converter.
With ECU controlled fuel injection, the "fuel cut" makes it a piece of cake...
