I got this error on my Skoda Fabia 2006 1.2 Bensin 3 cylinder (engine code BME), the car is **shaky on idle** like it is missing a cylinder, acceleration is non-linear, and fuel consumption is low at 5L/100km while the factory specs is 6l/100km

The current recurring error code is **P0172 System too rich**.

It doesn't have a Mass Air Flow sensor, it went 200,000 Km, and I replaced both Oxygen sensors 6 months ago.
The oxygen sensors was replaced when I got very high fuel consumption (+30 fuel trim) and **P0171 System too lean** in MIL.

After the o2 sensor replacement, I started to get **P0420 Catalyst efficiency below threshold**, but soon disappeared to be replaced with P0172 System too rich (current problem).

The MAP sensor reads 80 (I think) at 80km/h 2500rpm.

Short term fuel trim is almost always in minus between 0 and -8.

Fuel economy great, better than original specs.

Today I got **Cylinder misfire (I think it was P0301)**, which affected the engine greatly, I couldn't accelerate and the engine was very shaky, I turned off the engine and cleared it and every thing went back to where it was.

O2 sensor 1 gives oscillating signal between 0.1 and 0.8v but mostly on the high end of 0.5v, may be due to low refresh rate in the OBD scanner?

O2 sensor 2 gives between 0.1 and 0.3v plus small spikes at 80km/h 2500rpm.

Any idea what could be the reason?