Hi all, this problem had been bothering me for a month or so. My 2006 Prius started misfiring, with no codes, so I replaced all my spark plugs, ran a can of sea foam through the throttle body and fuel tank. Also replaced the air filter. The engine still misfired, and finally threw a code for cylinder 4, so I replaced the coil, cleared the DTC, and it ran smooth after. Now the main point. After a few days, the engine started misfiring again, and continued to do so on random occasions while the car is idling or charging the battery. My job right now involves a lot of standing by so I sit in my car with it in ready mode all day. It would come at random times, the engine would sputter and misfire for a second or two, then keep running like normal. No DTC came up, no misfires were detected. I ran a car scanner app through it via a Bluetooth adapter, in non continuous monitors it shows purge flow valve reading incorrect results. The emissions tab shows failed test for catalyst, oxygen, and evap system. I'm attaching all the screenshots to this post, please can someone take a look at it and tell me what's wrong with it? I'm good with replace parts by myself, but I need to know what it is.
Makes me wonder if you're experiencing an intermittent vacuum leak. Without having a chance to review documentation, I would imagine there is a testing sequence for the evaporative system. Perhaps this test sequence is introducing a large vacuum leak. Cracked hose or fitting in the test path? Resulting in, not only rough running, but also a failed test? Hopefully there's someone a bit more familiar with this portion of the car. This is definitely not my area of expertise.