2007 Prius Several months ago, my car would run rough at 75 miles an hour occasionally after I filled up. I chalked it up to bad fuel. Went to drive the car from one city to another and at 80 miles an hour the check engine light comes on and the engine is running really rough. It was the PO304 code. Limp it back home and went back the following weekend and trailered it to the new city. At 244,212 mi changed the plugs to new denso iridium from O'Reilly's, cleaned the MAF sensor and cleaned out the throttle body as well as checking the air filter. Did put a bottle of seafoam in the tank to help clear up any mess there, especially because the gas gauge isn't reading correctly either. The car ran great for a couple of weeks then today at 244,459 miles the dreaded PO304 code came back. Again it's intermittent with the car running rough for a few seconds before smoothing back out. It seems to stutter at speeds under 35 and then throws the code at speeds above 75 with the check engine light winking on and off. I'm scratching my head. I've attached the plugs in the order they were in the engine when I replaced them.
If you want, you can mark the ignition coils then swap #4 with another one- see if the miss follows the coil or not. Me, I would just replace all four with Toyota or Denso from a reputable source (then see how it operates). Also look closely at the white porcelain on your old #4 plug. You want to see if there is any black line (carbon track) going from the tip that goes into the coil down to the hex of the metal base. Posted via the PriusChat mobile app.
