idle troubleshooting on 1,8T Audi engine

[s.roul]

Hello

my 1,8T engine (code name AMK) has now got a unstable idle (changing
between 720 and 760 rpm) instead of a rock stable idle I got before.

Engine has now got 40 000 miles, I don't know what I should do... I(ve
already changed the MAF sensor but changed nothing to the idle
trouble.

I've seen on my VAG-COM that on channel 1, the lambda factor is always
changing between -3,9 and + 3,6... is it normal?
the lambda factor on channel 6 is rock stable at 1,6%.

Best regards,
 s.roul                          mailto:s.roul at free.fr