Replace spark plugs on the 2014-2019 Toyota Corolla 1.8L I4 engine to restore ignition performance and fuel efficiency.

Warnings

Tools required

Parts

• Spark plugs (iridium) × 4 — 90919-01253 or equivalent

Preparation

1. Ensure engine is cool to the touch
2. Park vehicle on level surface and engage parking brake
3. Gather all tools and verify spark plug gap specification (typically 0.043 inches/1.1mm for this engine)
4. Open hood and secure with prop rod

Procedure

1. 1

   Remove engine cover
   Grasp the plastic engine cover firmly and pull upward to release the retaining clips. The cover is held by push clips and does not require tools to remove. Set cover aside in a clean area.
2. 2

   Disconnect ignition coil connectors
   Locate the four ignition coils on top of the valve cover. Press the locking tab on each coil electrical connector and pull straight up to disconnect. There are four connectors total, one per cylinder.
3. 3

   Remove ignition coil bolts
   Using a 10mm socket, remove the single bolt securing each ignition coil. Keep bolts organized as they will be reused during reassembly.
   ℹ️Some model years may use slightly different bolt torque specs. Verify which ignition coil bolt spec applies to your specific year.
   Torque spec

   Ignition Coil Bolt10 Nm (8 lb-ft)
4. 4

   Remove ignition coils
   Grasp each ignition coil firmly and pull straight up with a twisting motion to break the seal. The coil boots may stick to the spark plugs due to heat cycling. Once removed, inspect each coil boot for cracks or damage.
5. 5

   Clean spark plug wells
   Use compressed air or a clean rag to remove any debris, dirt, or oil from around the spark plug wells. This prevents contamination from falling into the cylinders when plugs are removed.
   ⚠If oil is present in spark plug wells, valve cover gasket or seal replacement may be necessary.
6. 6

   Remove old spark plugs
   Using a 5/8" or 16mm spark plug socket with extension, carefully loosen each spark plug by turning counterclockwise. Once loose, unthread by hand to prevent cross-threading. Remove all four plugs and inspect electrodes and insulators for wear, deposits, or damage.
7. 7

   Gap new spark plugs
   Check the gap on each new spark plug using a spark plug gap tool. Verify gap matches specification (typically 0.043 inches or 1.1mm for this engine). Adjust if necessary by carefully bending the ground electrode. Do not force or pry against the center electrode.
   ℹ️Iridium plugs are pre-gapped from the factory but should still be verified before installation.
8. 8

   Apply anti-seize (optional)
   If using anti-seize compound, apply a small amount only to the first few threads of each spark plug. Avoid getting anti-seize on the electrode or insulator. Anti-seize is optional but recommended for aluminum cylinder heads to prevent thread galling.
9. 9

   Install new spark plugs
   Carefully thread each spark plug by hand into the cylinder head, turning clockwise. Ensure plugs thread smoothly without resistance. Once hand-tight, use the torque wrench and spark plug socket to tighten to specification. Use the aluminum head torque spec for this engine.
   ⚠️Cross-threading spark plugs can cause severe cylinder head damage requiring expensive repairs. Always start threading by hand.
   Torque spec

   Spark Plug19 Nm (14 lb-ft)
10. 10

    Apply dielectric grease to coil boots
    Apply a small amount of dielectric grease to the inside of each ignition coil boot. This prevents moisture intrusion and makes future removal easier.
11. 11

    Reinstall ignition coils
    Align each ignition coil with its corresponding spark plug and push down firmly until the coil seats completely. You should feel the boot snap onto the spark plug terminal. Install and hand-tighten the retaining bolt on each coil.
12. 12

    Torque ignition coil bolts
    Using a torque wrench with 10mm socket, tighten each ignition coil bolt to the specified torque. Follow a cross-pattern sequence (cylinder 1, 4, 2, 3) to ensure even seating.
    Torque spec

    Ignition Coil Bolt10 Nm (8 lb-ft)
13. 13

    Reconnect electrical connectors
    Reconnect the electrical connector to each ignition coil, pressing firmly until the locking tab clicks into place. Verify each connection is secure by gently pulling on the connector.
14. 14

    Reinstall engine cover
    Align the engine cover with the mounting clips and press down firmly until all clips engage with an audible click. Ensure cover is seated evenly.
    Torque spec

    Engine Cover Clips3 Nm (2 lb-ft)

Reassembly

1. Double-check that all electrical connectors are fully seated and locked
2. Verify engine cover is properly secured to all mounting points
3. Ensure no tools or parts are left in the engine compartment

Verification

• Start the engine and listen for smooth, even idle with no misfires or rough running
• Verify no check engine light or diagnostic trouble codes are present
• Allow engine to reach operating temperature and confirm smooth acceleration
• Inspect for any spark plug wire or coil boot arcing in darkness if available

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