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As title states: 2013 Toyota Corolla S

Had the check engine light come on just around a month ago and started idling rough. Pulled codes: P0301 (cylinder 1 has a misfire) and P219A (air to fuel ratio imbalance in bank 1).

I replaced the spark plug and ignition coil on the first cylinder (closest to the belt) and reset the codes by disconnecting the neg battery for a few hours. After a few miles the code P0301 popped up again, but no the P219A.

I've noticed the car "drinks" coolant now (I don't notice a leak) and the engine temp gauge runs very hot, full high. However, sometimes it'll drop all the way down to cold (like the engine is off) jumps a bit then back to high. I also notice a temp change in the heat/AC when that happens. Driving to work on a cold morning, it seems to stay at cold (0) the whole time.

I checked the engine oil today after driving on the interstate and it's clear.

tl;dr

  • Got codes for misfire and bad air/fuel mix on cylinder 1 / plus rough idle
  • Replaced spark plug and ignition coil
  • Misfire code popped back up
  • Sucking up coolant. Leak not apparent anywhere but not impossible
  • Engine temp stay all the way high but will drop to 0, jump a bit, the go back to 100.
  • Engine oil appears to be clear
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  • Welcome to Motor Vehicle Maintenance & Repair! Commented Dec 6, 2023 at 16:09

3 Answers 3

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It is physically impossible for the engine coolant temperature to change that rapidly when driving the car. Theoretically I guess a faulty thermostat could lead to occasionally cooling the engine too much, but this would be a gradual change, not a sudden change like you're experiencing.

This gives some clues. Your car has some electrical issue. The gauge is measuring the temperature with an electrical sensor, and something in the system isn't working now. It could be the supply of electricity to all of your car, or it could be just a poor contact at the temperature measurement circuit.

Since your car has misfire issues as well, the cause of misfire and apparent temperature jumping could be the same: some electrical issue is causing the ignition system to malfunction occasionally, and the same electrical issue could also cause jumping apparent temperature at the temperature gauge.

Since you already changed the spark plug and ignition coil, I would continue by diagnosing the electrical issue. If you can reproduce the temperature jumping, you could for example wire up a multimeter somewhere and see if you can see the voltage change at the same time. You could also check that your alternator and battery are working fine, and that the battery is well connected to the electrical system. Clean up the battery posts and clamps.

If the battery is original and has not been changed in the 10-year car lifetime, you could consider testing its health. At some point in near future, you are definitely going to need a new battery if your existing one is 10 years old.

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  • The thermostat confused me too. It would make toe sense if the car was overheating and/or the temp light was cutting on but it's not. The battery is semi-new but it's pretty bad corroded and gets corroded pretty quick after cleaning it in the past. Could a bad battery cause these issues/codes?
    – dcp3450
    Commented Dec 6, 2023 at 18:32
  • Most likely it would be caused not by a bad battery but rather poorly connected battery. So if it's newer than the car, don't change it yet, just clean all of the electrical connections as well as you can.
    – juhist
    Commented Dec 6, 2023 at 19:41
  • A simple solution of warm water and baking soda with a toothbrush will immediately dissolve dried battery acid forming on posts as the battery ventilates. Do not get any solution into battery cells - it neutralizes battery acid and will kill each cell and kill a battery. Plain water rinse and silicone grease applied against future corrosion. Treated felt battery post pads do the same. Connect a reader to display actual coolant temps after a warmup and compare it against t-stat rating. Replace it if in doubt. Check for coolant in engine oil via the oil dipstick.
    – F Dryer
    Commented Dec 6, 2023 at 22:30
  • @juhist this is my battery photos.app.goo.gl/NkLxtBFmZ4ECFTEu7 wound this likely cause misfire issues, you think?
    – dcp3450
    Commented Dec 6, 2023 at 23:32
  • @FDryer thanks, I'll try that.
    – dcp3450
    Commented Dec 6, 2023 at 23:32
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Firstly thermostats are so cheap and such an easy fix maybe start there to see if that helps at all with the irradic Temps. But It does seem like it's more likely an electrical issue.... just because it's easy and cheap maybe start with the battery. Poor grounds/grounding can cause all of the issues u mentioned due to spikes and drops in the voltage received by different components. Clean the battery ground cable and ones that run to the intake manifold. Make sure all are connected. These are sensor grounds and must be kept clean, also after you clean the terminals try to tighten them some make sure they don't wiggle at all. Just some easy things to check before you get into alternator and so on.

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  • Cleaned the terminals, had battery and alt tested, completely changed the negative battery cable. The code came back...
    – dcp3450
    Commented Dec 16, 2023 at 2:30
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So if your battery is saying charge and retest either alternator OR your battery terminals could still be the culprit...Electrolytes from the battery top can cause corrosion of the connections to the battery cables and prevent them from reaching a full charge, so the test would say charge and retest

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