How to Replace Ignition Coils on a 2018 Subaru Legacy (Fix Misfires & Rough Idle)
Step-by-step instructions with tools, parts list, safety tips, and ignition coil torque spec (7.5 Nm) for 2015, 2016, 2017, 2018, 2019
How to Replace Ignition Coils on a 2018 Subaru Legacy (Fix Misfires & Rough Idle)
Step-by-step instructions with tools, parts list, safety tips, and ignition coil torque spec (7.5 Nm) for 2015, 2016, 2017, 2018, 2019
🔧 Legacy - Ignition Coil Replacement
Your Legacy uses one ignition coil per cylinder (4 total). Replacing a failing coil can fix misfires, rough idle, flashing check-engine light, and loss of power.
Difficulty Level: Intermediate | Estimated Time: 1.0-2.0 hours
⚠️ Safety & Precautions
- ⚠️ Work on a cool engine; coils sit near hot metal parts.
- ⚠️ Disconnect the negative battery cable to prevent accidental shorting.
- ⚠️ Don’t pull on wiring—always release electrical connectors by the lock tab.
- ⚠️ Keep dirt out of the spark plug wells; debris can cause misfires.
🔧 Required Tools
You'll need the following tools for this repair:
- 10mm socket
- 3/8" ratchet
- 3" extension
- 6" extension
- Torque wrench (inch-pound or small Nm range)
- Flathead screwdriver
- Pliers
- Trim clip removal tool
- Dielectric grease
- Shop rags
- Nitrile gloves
- Safety glasses
🔩 Required Parts
HowToo sells all the parts you need for this repair:
- Ignition coil - Qty: 1-4
- Dielectric grease (small packet) - Qty: 1
📋 Before You Begin
- Park on level ground, shift to Park, and set the parking brake.
- Open the hood and let the engine cool fully.
- Disconnect the battery negative terminal using a 10mm socket and move the cable aside so it can’t spring back.
- Dielectric grease is non-conductive moisture protection.
- A torque wrench tightens bolts to a safe, exact force.
🔨 Step-by-Step Instructions
Follow these steps in order:
Step 1: Make room to reach the coils
- Remove the plastic engine cover (if equipped) by pulling it straight up with your hands (it’s held by rubber grommets).
- On the airbox side, loosen the intake hose clamp using a flathead screwdriver.
- Release any intake clips using a trim clip removal tool.
- If you still don’t have enough room on the battery side, remove the battery hold-down using a 10mm socket and lift the battery out carefully (it’s heavy).
Step 2: Unplug the ignition coil connector
- Locate the coil on top of the cylinder head (one coil per cylinder, two per side).
- Press the connector lock tab, then pull the connector straight off the coil.
- If it’s stuck, gently help it with a flathead screwdriver while pulling (don’t pry hard).
Step 3: Remove the coil hold-down bolt
- Remove the single hold-down bolt using a 10mm socket with a 3" extension.
- Set the bolt somewhere safe (dropping it is common in tight spaces).
Step 4: Pull the old coil out
- Twist the coil gently left-right, then pull it straight up to remove it from the spark plug well.
- Wipe any dirt around the opening using shop rags (don’t push dirt down the hole).
Step 5: Install the new coil
- Put a tiny smear of dielectric grease inside the rubber boot of the new coil (a pea-size is plenty).
- Push the coil straight down until you feel it seat onto the spark plug.
- Install the hold-down bolt by hand first to avoid cross-threading.
- Tighten the hold-down bolt with a torque wrench: Torque to 7.5 Nm (5.5 ft-lbs).
Step 6: Reconnect the coil connector
- Push the electrical connector on until it clicks.
- Lightly tug it to confirm it’s locked.
Step 7: Repeat for the remaining coils
- Replace the other coils one at a time so connectors don’t get mixed up.
- One-at-a-time prevents wiring mistakes.
Step 8: Reassemble what you removed
- Reinstall the intake duct/airbox pieces and tighten clamps using a flathead screwdriver.
- If removed, reinstall the battery and hold-down using a 10mm socket.
- Reconnect the battery negative terminal using a 10mm socket and tighten it snug (do not over-tighten).
- Reinstall the engine cover by pressing it down firmly by hand.
✅ After Repair
- Start the engine and let it idle for 1-2 minutes; it should run smoothly without shaking.
- If the check-engine light was on, it may take a few drive cycles to go out unless the code is cleared with a scan tool.
- Test drive 10-15 minutes and verify no hesitation under light acceleration.
- If you still have a misfire, the spark plug or injector on that cylinder may be the real cause.
💰 DIY vs Shop Cost
Shop Cost: $250-$650 (parts + labor)
DIY Cost: $60-$400 (parts only, depending on 1 vs 4 coils)
You Save: $190-$250+ by doing it yourself!
Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 1.0-1.5 hours.
🎯 Ready to get started?
HowToo makes it easy: same-day/2-day shipping on every part, plus all the tools and specialty tools you need! Check out the parts and tools sections below to add everything to your cart.

















