FJCruiser Running Rich

I encountered a similar issue with my 2012 Volvo C30. The symptoms you describe, such as reduced engine power, the check engine light, and rough running, align with my experience. Have you inspected the air filter? A clogged air filter can sometimes contribute to a rich mixture. Additionally, it may be prudent to examine the oxygen sensor readings, as a malfunctioning sensor can provide incorrect data to the engine control unit, leading to an improper fuel-air mixture.

Air filter is clean and I thought about the O2 sensor too. But wouldn't a bad O2 sensor usually throw a specific code? I'm not getting anything specific, just a general 'running rich' code. Is it possible that it's still the O2 sensor even without a dedicated code?

While a dedicated code for the oxygen sensor would be ideal for diagnostic purposes, it is indeed plausible that a malfunctioning sensor could contribute to the issue without triggering a specific fault code. Given the symptoms and the absence of other obvious causes, it might be most expeditious to have the fuel injectors inspected by a qualified technician. It appears that your vehicle needs professional attention.

Thanks for the advice! Turns out it was a defective fuel injector, just like I suspected. Got all the injectors replaced and the car is running perfectly again. Total cost was 515€. Appreciate the help!