Rich Gas smell coming from exhaust - 2010 base model

I don't have much experience with this myself, but from what I've read, the air/fuel mix is definitely the right track to chase. However it has a whole cast of characters that usually (I thought) come higher on the "whodunnit" list than your next steps above.

In your shoes I'd start my learning search at "running rich". Your issue is very likely not Prius specific -- it's a typical ICE issue and nothing to do with "hybrid". You started on that and already have a working model that says "I'm getting too much fuel -- is the computer asking for it because of bad sensor data, or getting it because of bad fuel delivery". That's a good starting place.

On the fuel delivery side, from what I've seen it's much less common to have the pump send too much than too little. An overzealous fuel pump is not usually a top suspect. Sort of wondering how you landed there.

On the sensor side, you could be under-measuring the fuel on the output side via O2/AFR (and so ask for more fuel than you needed). But you could instead be mis-measuring the air on the intake, or its temperature. I don't have an immediate grasp of this feedback loop, but I know it has more than one component to examine. They belong on the list of suspects too. (What is sort of Prius-specific is that the throttle body sucks up a lot of goop. It can coat the sensors and maybe cause the throttle plate to stick.)

Where possible you'd want to look for testing procedures rather than just replacing suspects one by one. Part swapping gets super expensive. Sometimes it's hard to do a good test, and an educated guess makes it a worthwhile gamble to try a parts swap. Zero shame in that IMHO. But at least check the repair manual for how to test the O2 sensors, for example.

DIY testing of sensors is going to require at least an OBD tool and maybe Techstream in some cases. You might need to learn about long term and short term fuel trims. There are lots of videos on that stuff.

Sensors like the MAF can at least be cleaned before trying replacement. Since that's actually relatively easy, you'd probably want to do it before trying something like replacement of an O2 sensor.

I'm not the guy to help you chase this whole thing, but maybe some guys with more wrench time can come up a better list of likely suspects...

 

Sometimes the o2 sensors are working fine. When there's an exhaust leak at the exhaust manifold it usually draws in ambience air (oxygen) which causes a lean reading on the o2 sensor. The computer will compensate by adding more fuel. Just something to consider.

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