🔧 IS - Spark Plug Replacement

On your IS, the spark plugs fire the air/fuel mixture. Worn plugs can cause rough idle, misfires, poor fuel economy, and sluggish acceleration. This job is done from the top of the engine by removing the ignition coils and swapping the plugs.

Difficulty Level: Intermediate | Estimated Time: 1.0-2.0 hours

Assumption: stock 2.0L turbo engine with coil-on-plug ignition.

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⚠️ Safety & Precautions

• ⚠️ Work on a fully cool engine to avoid burns and damaged threads.
• ⚠️ Keep dirt out of the spark plug holes; debris can damage the engine.
• ⚠️ Do not pull on wiring—release connectors by the lock tab first.
• ⚠️ Battery disconnect is not strictly required, but disconnecting the negative terminal prevents accidental shorts while unplugging coils.

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🔧 Required Tools

You'll need the following tools for this repair:

• 10mm socket
• 3/8" drive ratchet
• 3/8" drive torque wrench (10–30 Nm range)
• 5/8" spark plug socket
• 3/8" drive extension set (3" and 6")
• Small flathead screwdriver
• Pick tool
• Compressed air blow gun
• Shop vacuum
• Clean shop towels
• Nitrile gloves
• Safety glasses
• 10mm wrench

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Iridium spark plugs (OEM equivalent, correct heat range) - Qty: 4
• Dielectric silicone grease - Qty: 1

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📋 Before You Begin

• Park on level ground, shift to Park, and set the parking brake.
• Let the engine cool completely (warm aluminum threads strip easily).
• Open the hood and remove any loose items near the engine bay.
• If disconnecting the battery: use a 10mm wrench to remove the negative terminal and isolate it so it can’t spring back.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the engine cover

• Grip the cover firmly and pull straight up to release it from the rubber grommets.
• Set it aside where it won’t get stepped on.

Step 2: Unplug the ignition coil connectors

• Locate the 4 ignition coils on top of the engine (one per cylinder).
• Use a pick tool or small flathead screwdriver to gently lift/release the connector lock tab, then pull the connector straight off.
• “Ignition coil” = the plug’s electrical firing unit.

Step 3: Remove the ignition coils

• Use a 10mm socket and 3/8" ratchet to remove the bolt holding each coil.
• Twist each coil slightly, then pull straight up to remove it.
• Place coils in order so they go back in the same cylinder.
• During reassembly: Torque to 10 Nm (7 ft-lbs).

Step 4: Clean around the spark plug wells

• Use a shop vacuum to remove loose dirt from around each plug hole.
• Use compressed air blow gun to blow out the plug wells before removing plugs.
• Clean first to keep debris out of the cylinder.

Step 5: Remove the old spark plugs

• Install the 5/8" spark plug socket on a 3/8" extension and 3/8" ratchet.
• Lower the socket straight down onto the spark plug and loosen it counterclockwise.
• Once loose, spin it out carefully and lift it out with the socket.
• If a plug feels stuck: tighten slightly, then loosen again (don’t force it).

Step 6: Install the new spark plugs (by hand first)

• Compare the new plugs to the old ones (same length and thread size).
• Do not adjust the gap on iridium plugs; they are typically pre-set and the tips are fragile.
• Thread each new plug in by hand using the 5/8" spark plug socket and a 3/8" extension only (no ratchet at first).
• If it doesn’t thread smoothly, back it out and try again (this prevents cross-threading).
• Use a 3/8" drive torque wrench to tighten: Torque to 18 Nm (13 ft-lbs).
• No anti-seize on plated plug threads.

Step 7: Reinstall the ignition coils

• Apply a very small smear of dielectric silicone grease inside each coil boot (the rubber part that seals to the plug).
• Push the coil straight down until it fully seats on the spark plug.
• Install the coil bolts using a 10mm socket, then tighten with a torque wrench: Torque to 10 Nm (7 ft-lbs).
• Dielectric grease helps prevent moisture and sticking.

Step 8: Reconnect electrical connectors and reinstall the engine cover

• Reconnect each coil connector until it clicks into place.
• Reinstall the engine cover by aligning the grommets and pushing down firmly.
• If you disconnected the battery, reconnect the negative terminal using a 10mm wrench.

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✅ After Repair

• Start the engine and let it idle for 30–60 seconds; it should run smooth with no shaking.
• Listen for ticking/arcing sounds and re-check that every coil connector is fully clicked in.
• If you had a check engine light for misfire, use a scan tool to clear codes and confirm they don’t return.
• Take a short test drive and verify normal power under light acceleration.

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💰 DIY vs Shop Cost

Shop Cost: $250-$450 (parts + labor)

DIY Cost: $60-$140 (parts only)

You Save: $190-$310 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.

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