Today I checked all of the wires and hoses in the engine bay that were accessible without disassembling stuff and except for those injector wires and amp to coil wires that I aldready had shown here, they all look and feel pretty smooth, could not find any damages or brittleness, they all seem to sit tight.
But when I lay below the car to look for other stuff, I found this lonesome red connector in front of the the lower left wheel arch. Couldn't find its counterpart anywhere. Can anyone tell me what it is good for and where I can most likely find its counterpart? I guess it measures the air flow - maybe a cause for the bad idle? But shouldn't there be an error message on the dash then?