Phantom P0172 code has me bamboozled 😵💫
Recently I was fighting with recurring cylinder 1 & 2 misfire codes on my 2007 @ ~262K mi. after having performed a piston soak and installed new spark plugs in the months prior. (https://www.reddit.com/r/prius/s/dEqr5sPCMh)
I replaced all four fuel injectors a couple weeks ago - cylinders 1 & 2 cleared up, but then I got a new misfire on cylinder 4 and the P0172 code (system too rich bank 1), coupled with a strong gasoline smell. I double-checked my new fuel injectors, and a couple of the upper O-rings had gotten smashed and torn during installation. I replaced them, making sure to lubricate them well and handle them as gently as possible during installation. I also replaced the engine air filter, cleaned the MAF sensor, cleaned the throttle body, and ran a bottle of high- mileage Techron through the system.
It seemed like that solved the problem - it ran fine for 100+ miles, the gas smell disappeared, fuel efficiency jumped by 10-15 mpg, and I passed a smog test.
Literally one day later though, the P0172 code reappeared. I'm baffled at this point - the OBDII readouts on the MAF sensor, O2 sensors, throttle position, and air:fuel ratio all appear to be nominal, and I'm getting no gasoline smell anymore.
Anyone have any thoughts on what could still be causing P0172 or how to diagnose it - maybe a dirty O2 sensor? I'm gonna try another bottle of Techron, but I'm basically at my wit's end.