🔧 Impreza - Spark Plug Replacement

On your Impreza, the spark plugs sit in the cylinder heads on each side of the engine. Replacing them restores smooth starting, idle quality, fuel economy, and prevents misfires as the plugs wear.

Difficulty Level: Intermediate | Estimated Time: 1.5-3.0 hours

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⚠️ Safety & Precautions

• ⚠️ Let the engine cool fully before starting; the heads and exhaust get extremely hot.
• ⚠️ Disconnect the negative battery terminal to prevent accidental shorting and to protect electronics.
• ⚠️ Keep dirt out of the spark plug holes; debris can damage the engine.
• ⚠️ Do not pull on wiring—only pull on the coil connector body and coil body.
• ⚠️ Do not use anti-seize on modern plated spark plug threads unless the plug maker specifically says to; it can cause over-tightening.

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🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Nitrile gloves
• 10mm socket
• 12mm socket
• 3/8" drive ratchet
• 3/8" drive extensions (3" and 6")
• 3/8" drive swivel/universal joint
• 14mm thin-wall spark plug socket (magnetic or rubber insert)
• Torque wrench (3/8" drive, 10–30 ft-lb range)
• Small flathead screwdriver
• Trim clip remover
• Compressed air blow gun or canned air
• Flashlight
• Clean shop towels

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Spark plugs (iridium, correct fitment for 2.0L) - Qty: 4
• Dielectric grease - Qty: 1

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📋 Before You Begin

• Park on level ground, shift to Park, and set the parking brake.
• Open the hood and allow the engine to cool completely.
• Use a 10mm socket to disconnect the negative battery terminal (black “-”) and move it aside so it can’t spring back.
• Take a quick photo of hose routing.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the air intake ducting (for access)

• Use a flathead screwdriver to loosen the hose clamp(s) at the intake tube.
• Use a trim clip remover to pop any plastic clips holding the snorkel/duct.
• Lift the ducting out and set it aside.

Step 2: Create working room on the passenger side

• Locate the passenger-side ignition coil area (front-right side of engine).
• If the washer filler neck blocks access, remove its fastener(s) using a 10mm socket, then gently move it aside without kinking the hose.

Step 3: Create working room on the driver side

• Locate the driver-side ignition coil area (front-left side of engine).
• If the air box/ducting still crowds this side, reposition it as needed using a 10mm socket for any bolts and a flathead screwdriver for clamps.

Step 4: Unplug and remove ignition coils (one cylinder at a time)

• Unplug the coil electrical connector by releasing the tab with a small flathead screwdriver (gently) and pulling the connector straight back.
• Remove the coil retaining bolt using a 10mm socket.
• Pull the coil straight out. (An “ignition coil” is the part that sits on top of the spark plug and creates the high-voltage spark.)
• Do one coil/plug at a time to avoid mix-ups.

Step 5: Clean the spark plug well before removing the plug

• Blow out the spark plug well using compressed air blow gun or canned air and use a flashlight to confirm it’s clean.
• Wipe around the opening with clean shop towels.

Step 6: Remove the old spark plug

• Install a 14mm thin-wall spark plug socket on a 3/8" drive extension and swivel/universal joint (the swivel helps in tight spaces).
• Use a 3/8" drive ratchet to loosen the spark plug counterclockwise and remove it.
• If it feels stuck, stop and work it gently—don’t force it.

Step 7: Install the new spark plug

• Confirm the new plug is the correct type and appears undamaged. If it’s iridium, do not bend the tiny tip.
• Start the plug by hand using the spark plug socket and extension only (no ratchet at first) to prevent cross-threading.
• Once it’s seated, tighten with a torque wrench: Torque to 21 Nm (15 ft-lbs).
• Hand-starting is the best cross-thread prevention.

Step 8: Reinstall the ignition coil

• Apply a very small smear of dielectric grease inside the coil boot (dielectric grease helps prevent moisture and makes future removal easier).
• Push the coil straight onto the plug until fully seated.
• Install the coil bolt using a 10mm socket, then tighten with a torque wrench: Torque to 6.4 Nm (4.7 ft-lbs).
• Reconnect the coil electrical connector until it clicks.

Step 9: Repeat for the remaining 3 spark plugs

• Repeat Steps 4–8 for each cylinder, keeping hardware organized.

Step 10: Reassemble intake/removed items

• Reinstall the washer filler neck (if moved) using a 10mm socket.
• Reinstall the intake ducting and tighten clamps using a flathead screwdriver.
• Reconnect the negative battery terminal using a 10mm socket.

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✅ After Repair

• Start the engine and let it idle for 1–2 minutes. It should run smooth with no shaking.
• Listen for air leaks (hissing) around the intake tube you removed; re-tighten clamps with a flathead screwdriver if needed.
• If the check engine light is on or it runs rough, re-check that each coil connector is fully clicked in and each coil is bolted down.

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💰 DIY vs Shop Cost

Shop Cost: $300-$550 (parts + labor)

DIY Cost: $50-$140 (parts only)

You Save: $250-$410 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 1.5-2.5 hours.

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🎯 Ready to get started?

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