engine codes help

[alsgti]

hi guys i had my mk 4 gti in the garage this afternoon because its drinking too much petrol he put the the diognostic machine
and the codes were as follows
4480 :multiplicative mixture correction 1 too lean
40ab :fuel system bank 1 mix too lean
4086 :oxegen sensor 1 no signal
4646 :idel control adaption limit reached
he was only a trainee macanic and the place was closing so any ideas people pls let me know
i now what you all will be saying yes its a 20ltr gti i now they use a lot but mine just takes the p.ss 

[topher]

replace the o2 sensor and get someone with a bit more know-how to log the data from the airflow meter while driving because that could be goosed too