🔧 GS - Spark Plug Replacement

You’ll be replacing all six spark plugs and reinstalling the ignition coils. On your GS, the front bank is easy to access, but the rear bank typically requires removing the upper intake manifold to reach the three rear plugs.

Difficulty Level: Intermediate | Estimated Time: 2.5-4.0 hours

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⚠️ Safety & Precautions

• ⚠️ Work on a fully cool engine to avoid burns and stripped threads.
• ⚠️ Disconnect the battery negative terminal to prevent accidental short circuits.
• ⚠️ Keep dirt out of the intake—cover open ports with clean rags immediately.
• ⚠️ Do not over-tighten spark plugs; aluminum heads strip easily.
• ⚠️ Use only OEM-spec iridium plugs; wrong plugs can cause misfires.

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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", 6", 10")
• 3/8" drive wobble extension
• 14mm thin-wall spark plug socket (3/8" drive)
• Torque wrench (5–80 Nm range)
• Flat trim/panel tool
• Needle-nose pliers
• Small pick tool
• Compressed air blow gun
• Shop rags
• Magnetic pickup tool

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Iridium spark plugs (OEM-spec) - Qty: 6
• Upper intake manifold gasket set - Qty: 1
• Throttle body gasket - Qty: 1
• Dielectric grease - Qty: 1

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📋 Before You Begin

• Park on level ground, set the parking brake, and open the hood.
• Let the engine cool completely (at least 1 hour after driving).
• Use a 10mm socket to disconnect the battery negative terminal and isolate it so it can’t spring back.
• Plan your layout: set bolts in labeled groups (front bank, intake, throttle body). Prevents “mystery bolts” later.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the engine cover and intake ducting

• Lift off the plastic engine cover (it pulls up).
• Use a 10mm socket and needle-nose pliers to loosen/remove the air intake duct/hoses as needed for access.
• Use a flat trim/panel tool to release any clips without snapping them (a trim tool is a plastic pry tool that won’t gouge parts).

Step 2: Replace the front-bank spark plugs (easiest side)

• Unplug each ignition coil electrical connector using a small pick tool to lift the lock tab if it’s stubborn.
• Remove each coil hold-down bolt with a 10mm socket.
• Pull the coil straight up and out.
• Blow out the spark plug well with compressed air blow gun so dirt can’t fall into the cylinder.
• Remove the spark plug using a 14mm thin-wall spark plug socket with 3/8" drive extensions and a 3/8" drive ratchet.
• Install the new plug by hand first using the socket/extension only (no ratchet) to avoid cross-threading.
• Tighten with a torque wrench: Torque to 18 Nm (13 ft-lbs).
• Add a tiny smear of dielectric grease inside the coil boot (dielectric grease helps prevent moisture and makes future removal easier).
• Reinstall coils and bolts: Torque to 10 Nm (89 in-lbs), then reconnect connectors.

Step 3: Remove the throttle body (to access the rear bank area)

• Unplug the throttle body electrical connector using a small pick tool if needed.
• Remove throttle body fasteners with a 10mm socket.
• Move the throttle body aside carefully (do not force the wiring).
• Remove and discard the old throttle body gasket.

Step 4: Remove the upper intake manifold (rear-bank access)

• Disconnect any small vacuum/PCV hoses using needle-nose pliers as needed, and mark them with tape if helpful.
• Use a 12mm socket with a 3/8" drive ratchet and extensions to remove the upper intake manifold bolts/nuts.
• Lift the manifold off carefully.
• Immediately cover the exposed intake ports with shop rags so nothing falls in.
• Remove and discard the old upper intake manifold gaskets.

Step 5: Replace the rear-bank spark plugs

• Remove ignition coil connectors using a small pick tool if the lock tabs are tight.
• Remove coil bolts with a 10mm socket and pull coils out.
• Blow out each plug well using compressed air blow gun.
• Remove plugs using a 14mm thin-wall spark plug socket, wobble extension, and 3/8" drive ratchet.
• Install new plugs by hand first, then tighten: Torque to 18 Nm (13 ft-lbs).
• Reinstall coils and bolts: Torque to 10 Nm (89 in-lbs), reconnect connectors.

Step 6: Reinstall intake manifold and throttle body

• Remove the shop rags from the intake ports.
• Install new upper intake manifold gaskets.
• Set the manifold in place and hand-start all bolts/nuts.
• Tighten manifold fasteners evenly using a 12mm socket and finish with a torque wrench: Torque to 21 Nm (15 ft-lbs).
• Install the new throttle body gasket and reinstall the throttle body using a 10mm socket.
• Tighten throttle body fasteners with a torque wrench: Torque to 10 Nm (89 in-lbs).
• Reconnect all hoses and electrical connectors.

Step 7: Reassemble intake ducting and reconnect the battery

• Reinstall any intake ducting/air tubes using a 10mm socket and secure clamps.
• Reinstall the engine cover (press down to seat it).
• Reconnect the battery negative terminal using a 10mm socket.

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✅ After Repair

• Start the engine and let it idle for 2–3 minutes. A slightly rough idle for a few seconds can be normal while it relearns.
• Listen for hissing (vacuum leak). If you hear it, recheck intake hoses and manifold seating.
• If the check engine light comes on, recheck coil connectors first (most common mistake).
• Do a short test drive, then recheck for any loose clamps or abnormal smells.

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💰 DIY vs Shop Cost

Shop Cost: $450-$850 (parts + labor)

DIY Cost: $90-$220 (parts only)

You Save: $360-$630 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 2.5-4.0 hours.

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🎯 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.

Assumption: Your GS uses the common rear-bank-under-intake layout; steps reflect that configuration.