Hi there, the car works now!
So few input for who's looking to fix their 3Ls:
-RTFM! 12 was for me bad gear actuator and/or bad adjustment (also RTFM! 9) and/or remaining air in the pipes.
-When you indeed change the gear actuator etc, the first basic settings will naturally fail because some air remain in the pipe, but as the gear (and clutch) actuator will make quite few moves during basic settings, the next try will be OK on this side (check the green oil level at that point, unplug the pump and open the pressure accumulator in order to do that).
-After installing a gear actuator, leave gear selector shaft on Neutral, and switch on with the gear lever on 'N'. It make no difference on calibration (visible on Block 15), it's just that the Transmission Computer will not try to change too many gears before you do the basic settings.
-Errors 00844 (F257) & 00845 (F258) did not matter, I just delete them prior to basic settings.
-Be sure to have good voltage in your battery, slow response from calculators happen with too low voltage.
I notice also a poor response in the 2 first minute after reconnecting the battery.
-Prior to all that, using VCDS, the letters about the Transmission calculator was corrupted, with "no communication" errors from the engine calculator (error 01312/01314) or the ABS calculator 01316 (errors also stored in the Instrument calculator).
The only solution was to swap the Transmission calculator, also check relay 109 and 424 and fuse 31.
-On my 100K/160.000kms gear box, the neutral/natural position was not on front of the first gear (that's why the rod was looking too short, and was then OK by less than 1mm with another gear actuator). So of course when you adjust with no tension on the vertical rod, the basic settings will then fail (again, as not on front of first gear). But your adjustment will be accepted if reverse light switch on at test 5 of the 28, what ever was the tension on vertical rod during adjustment in this case. I manage to find the right adjustment by engaging manually the Reverse (with no pressure in the system by opening the accumulator) and then adjust with the top arm at the highest position (without using force, just push gently the vertical rod to the highest position and tight the 13mm nut). I then reconnect the pump and do the basic settings ignoring the "Adjust!" invitation.
- Not all Lupo's Transmission Computer have the Creep point adaptation, mine shows "Group 25 unavailable", in current car, as it was in the previous Lupo. I got confirmation the early models might not have this function. Audi A2 appears a year after so should have it. Creep point adaptation is somehow included here to the step 1, where you set the correct voltage value for the clutch travel sender -G162-.
And better be conservative with a value as low as 1.7V than over 2V. Low value open the clutch earlier, so if you don't have too much slip, it will manage your gearbox better.
- Last, so far, when you see the first gear constantly been ejected (the gear actuator will automatically try to put it back, and so on), and no possibility to select reverse, but have no error on VCDS, and all gears passing OK with engine off; you can start to suspect your gearbox and/or the clutch actuator. It happen to me with a 20.000km FLE from 2004! At least the gear actuator or the electric wiring was not the cause. But I need to do more kilometers to be 100% sure, to confirm this problem is gone. Will also post here once this gearbox will be opened and inspected.
Voila; and good luck!