ECU problem?

GRiSO 1200 (2010) did not run well. Got ecu error 62. As a consequence I opened several connections and also checked stepper motor hoses and connections to ecu. I have AFR clock and said around 11-12 before tried to find reason for the error. Now after checking several things AFR says around 17-20 - very lean. Today I connected Guzzi Diag, before starting engine looked good, after starting engine e.g. voltage reading was 5888.00V, rmin 58880 etc. Does not look good, ECU dead or something else?

Has it been rollerised?

If you can start the engine, the ECU is not dead. First thing to do is go back and reseat every connector you opened. Then, check the pins on the ECU, as well as making sure the ground connection on the ECU is clean and tight. Also check/clean the ground on the starter.

It has not been rollerised, however some parts changed related to valves before 18000 km - I bought this when 18000 km on clock.
What I did not tell (to make long story short), after checking and opening several connections plus stepper + ecu connections/pins I started the engine, error code (62 = stepper motor gnd) disappeared, warmed motor up, rode 3 km. Everything looked great until I turned back to front yard - AFR moved from around 14 to 20. I turned off the engine immediately. On the following day (yesterday) connected GuzziDiag showing crazy readings, almost all starting 5888...

Starter motor was removed and cleaned a year ago including connections.

Well there's little point in fixing anything until it's rollerised but stepper has been flagged and I'd wonder about the O2 sensor as well.

Ok, thank you. O2 sensor has been removed and set "lambda off" with guzzidizag.