🔧 Spark Plugs - Replacement

On your Avalon, the front 3 spark plugs are easy to reach, but the rear 3 sit under the upper intake manifold (the “plenum”), so you’ll remove the intake top to access them. Replacing all 6 at once prevents repeat labor and helps avoid misfires and rough running.

Difficulty Level: Intermediate | Estimated Time: 2.0–4.0 hours

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⚠️ Safety & Precautions

• ⚠️ Work on a fully cool engine to avoid burns and damaged threads.
• ⚠️ Keep dirt out of the intake—cover openings with a clean towel once the plenum is off.
• ⚠️ Do not pry on plastic connectors; release the lock tab first.
• ⚠️ Battery disconnect is not required, but if you’re nervous around electrical connectors, disconnect the negative terminal using a 10mm wrench.

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🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Nitrile gloves
• Fender cover
• 1/4" drive ratchet
• 3/8" drive ratchet
• 3/8" drive torque wrench (10–30 ft-lbs range)
• 10mm socket
• 12mm socket
• 14mm thin-wall spark plug socket (3/8" drive)
• 3/8" drive extension set (3", 6", 10")
• Universal joint swivel (3/8" drive)
• Flat-blade screwdriver
• Trim clip tool
• Long needle-nose pliers
• Compressed air blow gun
• Shop towels
• Paint marker

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Spark plugs (OEM-spec iridium) - 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, shift to Park, and set the parking brake.
• Let the engine cool completely (at least 1–2 hours after driving).
• Use a paint marker to mark any vacuum hoses you remove so they go back to the same place.
• If disconnecting the battery: loosen the negative terminal with a 10mm socket 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

• Pull straight up on the engine cover to release it from its rubber grommets.
• Set it aside on a clean surface.

Step 2: Unplug and remove the front-bank ignition coils (front 3 plugs)

• Unplug each coil connector by pressing the lock tab and pulling straight back.
• Remove each coil hold-down bolt using a 10mm socket.
• Pull each coil straight up and out, then set them in order. Keep coils in the same cylinders.
• During reassembly: Torque coil bolts to 10 Nm (89 in-lbs).

Step 3: Remove the front-bank spark plugs

• Blow out each spark plug well using a compressed air blow gun so dirt can’t fall into the cylinder.
• Remove each plug using a 14mm thin-wall spark plug socket with a 3/8" drive extension and 3/8" drive ratchet.
• Spark plug socket = a deep socket with a rubber insert that grips the plug so you can lift it out.

Step 4: Remove the air intake duct (to access the plenum)

• Loosen the intake hose clamps using a flat-blade screwdriver.
• Unclip/unbolt any intake duct fasteners using a 10mm socket.
• Lift the duct out and set it aside.

Step 5: Disconnect the throttle body electrical connector and hoses

• Unplug the throttle body connector (press the lock tab, then pull straight off).
• If any small hoses/lines block access, release clamps using long needle-nose pliers and move the hose aside.
• Use shop towels to catch any small drips.

Step 6: Remove the throttle body (recommended for room and gasket replacement)

• Remove the throttle body mounting bolts using a 10mm socket.
• Remove the throttle body and the old gasket.
• During reassembly: install a new gasket and torque throttle body bolts to 10 Nm (89 in-lbs).

Step 7: Remove the upper intake manifold (plenum)

• Disconnect any remaining vacuum/PCV hoses from the plenum using long needle-nose pliers (move clamps back first).
• Unplug any sensors/solenoids attached to the plenum by releasing the lock tab.
• Remove the plenum mounting bolts/nuts using a 12mm socket and 3/8" drive ratchet.
• Lift the plenum off carefully.
• Immediately cover the lower intake openings with shop towels.
• During reassembly: install new plenum gaskets and torque plenum bolts/nuts to 21 Nm (15 ft-lbs).

Step 8: Unplug and remove the rear-bank ignition coils (rear 3 plugs)

• Unplug each rear coil connector.
• Remove each coil hold-down bolt using a 10mm socket.
• Pull coils straight up and set them aside in order.
• During reassembly: torque coil bolts to 10 Nm (89 in-lbs).

Step 9: Remove the rear-bank spark plugs

• Blow out the plug wells using a compressed air blow gun.
• Remove plugs using the 14mm thin-wall spark plug socket, a universal joint swivel, and the needed 3/8" drive extensions.
• Turn steadily. If one feels stuck, stop and work it gently to avoid thread damage.

Step 10: Install the new spark plugs

• Compare new vs old plugs to confirm matching length and tip style.
• Start each plug by hand using the spark plug socket and a 3/8" drive extension (no ratchet yet) to prevent cross-threading.
• Tighten with a 3/8" drive torque wrench: Torque spark plugs to 18 Nm (13 ft-lbs).
• Apply a small amount of dielectric grease inside each coil boot before reinstalling coils.

Step 11: Reassemble the intake and intake duct

• Remove the shop towels from the intake ports.
• Install the plenum with new gaskets and tighten fasteners evenly using a 12mm socket, then torque plenum bolts/nuts to 21 Nm (15 ft-lbs).
• Reinstall the throttle body with a new gasket using a 10mm socket, then torque throttle body bolts to 10 Nm (89 in-lbs).
• Reconnect all hoses and electrical connectors until they click.
• Reinstall the air intake duct and tighten clamps using a flat-blade screwdriver.

Step 12: Reinstall the engine cover

• Press the cover straight down until it seats into the grommets.

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✅ After Repair

• Start the engine and let it idle for 1–2 minutes.
• Listen for a hissing sound (vacuum leak) and check that the idle is smooth.
• If you disconnected the battery, the idle may relearn for a few minutes.
• Test drive 10–15 minutes, then recheck for any warning lights.
• If you have a scan tool and had a misfire light before, clear codes and confirm none return.

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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 2.0-3.5 hours.

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🎯 Ready to get started?

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