I'm trying to understand the advantages of lambda and MAF while I drive an old car, those parts are worn.
How come I have loss in fuel efficiency while there is no gain in performance?
The engine ECU uses the readings from these sensors to get the fuel to burn as weak as possible while still being efficient and keeping the burn temperatures safe for the engine.
If the MAF and O2 sensors are not giving valid signals, the ECU will have to err on the side of caution and make the fuel mixture rich to ensure that the engine cannot be damaged by excessive burn temperatures. This will cause the engine to use more fuel and since it is now not burning the fuel at maximum efficiency, then you may even feel a drop in power output.
Burning more fuel does not always equate to more power, you need to add the correct amount of oxygen to make good use of the fuel. Adding too much oxygen can also cause excessive heat and a more explosive mixture which is not good for the engine.