Engine test.

Hello, guys.

I thought before I go around like that I would rather ask again in the forum!
I have the following problem: after I had a new Labdasonda installed in the summer, I had absolute dream consumption values, but only 2 months long. After that, he suddenly got two liters more on a hundred kilometers. When exchanging spark plugs, I then noticed that they are pretty black, i.e. it runs pretty fat! Error memory says3 Error:00525 003 Lambda probe no signal G39, 00537 008 Lambda control limit exceeded ; 00513 003 encoder for engine speed no signal.. I had extra mass cables laid, no success, unfortunately. Up to now, the fun cost me 280 euros for nothing, and a lot of trouble with the incompetent workshop.That has led me to the fact that I don't dare to go into a place anymore, with the fear that they will then go on trouble-shooting again for hours! But since the latest comes a jerking at Tellast, so around the 2000 rpm people tell me, what can I do?!

Thanks in advance for advice..

Rainer