I recently got a flashing CEL and the code P0301 on a road trip on the way home from Detroit. After finding out the code was for Cylinder 1 Misfire, I had a really hard time finding information and others with experience with this code. Found many threads about it, and how it had the owner stumped but not too many actual results. Hopefully this will help someone else in the future.
As stated previously, I got a code P0301 on the way home from a small road trip accompanied by a flashing CEL. It would flash and then go off for a while, or flash and then stay on for a while. I also noticed a bad hesitation during acceleration that seamed to get much better after 2,000 RPM, but not go away. Once back in town I had Advance Auto Parts pull the code and it was Cylinder 1 Misfire.
My first step was to replace the plugs and wires. They needed done anyways, so this seemed like a logical place to start. Unfortunately plugs and wires did not fix the problem. My initial thinking after this was that it was not a coil pack. I figured since each of the three coil packs fired 2 cylinders, the coil pack going bad would cause two misfires rather than one. I'm still not sure if this is the correct thinking or not, but I decided to rule it out officially. I removed the coil pack from cylinder number 1 and switched it with cylinder number 5 coil pack. Then headed to AAP again and had the code pulled. Still a cylinder 1 misfire. Coil pack ruled out.
Next step was to test the fuel injector. I bought a digital multi-meter from Harbor Freight on sale for $1.99. I was unsure how to test the injector, so after a google search I came across a couple of YouTube videos showing exactly how. If you never have looked up these type of videos on youtube before, they can be very helpful. I tested the resistance on the cylinder 1 fuel injector and the multi-meter wouldn't read anything. In general, injectors should be between 11 and 18 ohms, with more specific parameters per model. I also tested injector 3, which read 15.3; and injector 5, which read 14.8. This was all the information I needed. I called Toyota and ordered the injector. Changing the injectors on the passenger side of the engine is not a difficult job if you know your way around the engine bay decently enough. The drivers side is much more difficult and involves removal of the intake manifold.
For the 3 injectors on the passenger side I first had to remove the intake tube between the throttle body and MAF sensor. After this I had to remove the throttle body. If you have never done this, you need to be patient as it is somewhat involved. There are 3 cables on the front that need to be removed, 2 coolant lines, and a vacuum line from the IAC valve (located on the bottom of the TB), a clip for the IAC, clip for the TPS, and then 2 nuts and 2 bolts and you can remove the TB. After removal of the throttle body you have all the access you need to the fuel rail and injectors. There are 2 17mm banjo bolts on both sides of the fuel rail. You can remove these, and then 2 12mm bolts holding the actual fuel rail on. It may take some jiggling but you can then pull the fuel rail up and change the bad injector.
NOTE: EVEN ON THE INJECTORS THAT ARE NOT BAD, YOU NEED TO REPLACE THE O-RINGS ON THE TOP AND BOTTOM. THEY WILL LEAK!
Once the bad fuel injector has been replaced you can put everything back together the way you took it apart (it is also recommended that you change the TB gasket). Start the vehicle and check for leaks on all the injectors. I would also recommend checking the injectors again a couple times over the next day or so to make sure no leaks develop as the engine heats up and pressure builds.
Again, hopefully this helps someone at some point. Sorry there are no pictures but I didn't even think to take any during the process. Feel free to ask any questions and I'll answer them as best I can. Thanks!
