After 137,000 km range, my Mercedes Benz E300 W212 M272 engine gets the warning light. With code P0172 System too rich. DTC code 0746 and 0750 the mixture is too rich. Looking at the data stream, seem like the oxygen sensors are good. The suspect is the MAF sensor. The data stream reading shown too high air flow rate of 6 g/s at idle rpm. Inspection the sensor shows a lot of dust collected on the sensor mirror. After done cleaning the sensor, the air flow rate drop to 3.7 g/s at slightly lower idle rpm of 600 rpm. The results were better than expectation. The engine runs smoother, less vibration. The fuel consumption slightly drop from 11 to 10 l/100km. Thank you for watching.