F800gs going leaner and leaner

[Urbandrag]

Hi there,

I just performed some service in an 800gs.
I left the bike without the battery for several weeks.
Few days ago I put the bike in one piece and when I started the engine for the first time, the afr goes leaner and leaner until it stops according to plot o2 chart.
I just checked for air leaks because I heard a like a whustle sound coming from the throttle bodies, I even replaces tb clamps, and I can't find anything.
I've read in a forum that the problem is like the ecu forgets some settings by being unplugged too long from power. And it solves itself by riding several tanks.
Any suggestion?