how to fix a misfire in my Toyota Corolla E170 (2013-2019) that's throwing P0301 code

Solution

1. Preparation

• Tools Required: OBD-II scanner, socket set, torque wrench, compression tester, multimeter.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the engine to cool before starting work.

2. Replace Spark Plug

1. Remove the engine cover (if applicable) using a socket set.
2. Disconnect the ignition coil connector from the spark plug.
3. Remove the ignition coil from cylinder 1 by unscrewing the mounting bolts.
4. Use a spark plug socket to carefully remove the spark plug from cylinder 1.
5. Inspect the spark plug for wear or damage; replace if necessary with a new spark plug that matches OEM specifications.
6. Install the new spark plug, ensuring the gap is correct according to the manufacturer’s specifications (typically around 0.043 inches for Toyota).
7. Reinstall the ignition coil and securely fasten the bolts.
8. Reconnect the ignition coil connector.

3. Replace Ignition Coil

1. If the misfire persists after replacing the spark plug, remove the ignition coil from step 2.
2. Replace the ignition coil with a new one that meets OEM specifications.
3. Reinstall the ignition coil and reconnect the electrical connector.

4. Clean/Replace Fuel Injector

1. If misfire is still present, remove the fuel injector from cylinder 1.
2. Inspect the injector for clogs or damage; clean or replace it as necessary.
3. Reinstall the fuel injector and ensure it is seated properly.

5. Perform Compression Test

1. If all previous steps do not resolve the issue, perform a compression test on cylinder 1.
2. Insert the compression tester into the spark plug hole and crank the engine to obtain a reading.
3. Compare the reading to the manufacturer specifications (usually between 180-200 psi).
4. If compression is low, further investigation into the engine internals may be required.