Hello, after doing several tests incluiding from simple things to elaborated as testing another wiring harness, i found that the problem was a faulty Throttle body :S
It was a little hard to find the fault as the first original TB was able to run the adaptation OK and a second TB too, so i discarded the TB as the cause. It was after trying a third known good TB that we can solve the .75 lambda issue at idle.
One thing that we noted is that while with the faulty TB, if we allowed to enter just a little more air to the engine by the brake booster hose connection, the lambda at idle went normal. After that we tried the 3rd TB with success.
I want to mention how we solve this, so you don´t have to go crazy like us with a fault like that!
Thanks to everyone for your help!
Interesting, anyway to foolproof throttle body with me7logger or vcds?