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Q: I have logged fault codes P0300, P0301, and P0303. What is the problem? on 2002 Toyota Highlander

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Misfires are noticeable. I don't feel like I can go over 50mph. These displayed about 20 miles after filling up a nearly empty tank. I can't siphon a gas sample to check for water because a rollover spillage blocking device is in the tank. I replaced plugs and swapped the coils to no effect. I cleaned the MAF to no effect. I can't hear or see an intake problem. I have the Torque Pro app but don't really know what to look for to diagnose this problem. I did notice my STFT2 was over 20% while STFT1 was -5%, but MAF at warm idle is 2.4g/s, load at WTO is 85%. If you could give me pointers on how to check 02 sensors or other possible culprits with the Torque Scanner app, I'd be very grateful!
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You did swap the known good coils, 2 & 4 with the 1 & 3 coils i assume? Back to the basic tests, compression, vacuum, ignition and fuel. You should find the problem with those tests! If not equipped to complete, get some hands-on help.
Thanks to all of you for your help! I ended up getting help from a friend who is a mechanic. He first drained the fuel tank and put in some shell premium. Following that the only code that remained was P0303. So he swapped injectors 1 and 3 and the code moved to 1. He installed a new injector in 1 and everything appeared fixed. Except a day later I was driving along and got 2 cat codes, P0420 and another. I don't happen to recall exactly right now. But I was afraid of something like this because I drove about 100 miles with those misfires!! So now I have some more research to do. I am really hoping this doesn't lead to a new cat before christmas!! Not at all what I asked Santa for.
Have the 02 sensors tested with a scan tool, mechanic can tell from live data if cat is failing. Possible downstream 02 fault.
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You have the information that we need to start testing for the misfire, and the bank to bank fuel trim suggests at the least a potential downstream O2 sensor fuel trim issue, or it could be an airflow problem such as a cam out of time or a restricted exhaust on just one side. The bank taking away fuel would potentially be the side that isn't breathing as good as the other bank. Miss-fires kill catalysts, this needs addressed before it gets worse.
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