w203 2005 201C truble code problem

[oink2002]

c w203 2005 1.8 kompresor
201c selfadaptation of mixture formation; The mixture is too rich in the part load range.

o2 sensor stay 1.4v,
i have replaced o2 sensor and nothing changed, no vacum leak, no exchause leak, MAF ok, car run perfect

can someone give me e direction or solution please?

Check the air bypass between cylinderblock and kompressor. There is a plastic hose guided through a hole in the block. the diameter of the pipe is ~10mm. To get good access , the kompressor should be removed. You can see this section in EPC.