🔧 Sienna - Spark Plug Replacement

On your Sienna, the front 3 spark plugs are easy to reach, but the rear 3 sit under the upper intake manifold (plenum), so you’ll remove the plenum to access them. Replacing worn plugs restores smooth idle, power, and fuel economy, and helps prevent misfires.

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 negative battery cable to prevent accidental shorts and throttle body issues.
• ⚠️ Do not use anti-seize on Toyota-plated spark plugs unless the plug maker explicitly requires it.
• ⚠️ Keep dirt out of the intake ports—cover openings immediately after plenum removal.

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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" ratchet
• 3/8" torque wrench (10-80 Nm range)
• 6" extension (3/8")
• 10" extension (3/8")
• 3/8" universal joint (specialty)
• 14mm thin-wall spark plug socket (3/8")
• Flathead screwdriver
• Hose clamp pliers (specialty)
• Trim clip tool
• Painter’s tape
• Shop towels

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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 and set the parking brake.
• Let the engine cool completely.
• Use a 10mm socket to disconnect the negative battery terminal and isolate it so it can’t spring back.
• Set painter’s tape aside to label any vacuum/EVAP hoses you remove so they go back to the same spot.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the engine cover and open up access

• Pull up to remove the plastic engine cover (it’s held by grommets).
• Use a flathead screwdriver to loosen the air intake hose clamp(s) at the throttle body.
• Unclip/remove the intake ducting as needed and set it aside.

Step 2: Remove the front-bank ignition coils (front 3 plugs)

• Unplug each coil connector by pressing the tab and pulling straight back.
• Use a 10mm socket to remove the ignition coil hold-down bolt for each coil.
• Twist the coil slightly and pull it straight up to remove it.
• Keep coils in order, one per cylinder.

Step 3: Remove the front-bank spark plugs

• Put the 14mm thin-wall spark plug socket on a 6" extension and 3/8" ratchet.
• Break each plug loose, then remove it fully by hand with the ratchet.
• Install the new plug by threading it in by hand first using the socket/extension (no ratchet at first) to avoid cross-threading.
• Tighten with a 3/8" torque wrench: Torque to 18 Nm (13 ft-lbs).

Step 4: Reinstall the front-bank coils

• Apply a very small amount of dielectric grease inside each coil boot (just a thin wipe).
• Push the coil straight down onto the plug until fully seated.
• Install the coil bolt using a 10mm socket, then tighten with a 3/8" torque wrench: Torque to 10 Nm (89 in-lbs).
• Reconnect the coil electrical connectors.

Step 5: Disconnect hoses/connectors and remove the upper intake manifold (rear-bank access)

• Unplug the throttle body electrical connector(s) and any nearby harness connectors that prevent lifting the plenum.
• Use hose clamp pliers to release spring clamps and disconnect the PCV/vacuum/EVAP hoses attached to the plenum.
• Use painter’s tape to label hoses if more than one comes off.
• Remove plenum mounting fasteners using a 10mm socket and/or 12mm socket (varies by fastener location).
• Lift the plenum off carefully. If it sticks, gently wiggle—do not pry on sealing surfaces with force.
• Immediately place shop towels over the exposed intake ports to keep hardware/dirt out.
• A universal joint helps rear fasteners.
• Note: A 3/8" universal joint is a swivel adapter that lets the socket bend to reach awkward bolts.

Step 6: Replace the rear-bank spark plugs (rear 3 plugs)

• Remove rear ignition coils the same way as the front: unplug connectors, remove coil bolts with a 10mm socket, pull coils out.
• Remove each rear spark plug using the 14mm thin-wall spark plug socket, 10" extension, and 3/8" universal joint as needed.
• Install each new plug by hand first, then tighten with a 3/8" torque wrench: Torque to 18 Nm (13 ft-lbs).
• Reinstall coils and tighten coil bolts: Torque to 10 Nm (89 in-lbs).
• Reconnect all coil electrical connectors.

Step 7: Reinstall the upper intake manifold with new gaskets

• Remove the old upper intake manifold gasket(s) and install the new ones (make sure they sit flat in their grooves).
• If the throttle body was separated, replace the throttle body gasket before reassembly.
• Remove the shop towels from the intake ports.
• Set the plenum back into place carefully without pinching any wiring or hoses.
• Install all plenum fasteners finger-tight first, then tighten evenly using a 10mm socket/12mm socket and finish with a 3/8" torque wrench: Torque to 21 Nm (15 ft-lbs).
• Reconnect all vacuum/EVAP/PCV hoses using hose clamp pliers and remove your tape labels.
• Reconnect throttle body and any other electrical connectors.

Step 8: Reinstall the intake duct and engine cover

• Reinstall the intake ducting and tighten the clamp(s) using a flathead screwdriver.
• Reinstall the engine cover by pressing it down onto the grommets.

Step 9: Reconnect the battery

• Reconnect the negative battery terminal using a 10mm socket.

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✅ After Repair

• Start your Sienna and let it idle for 1–2 minutes. A slightly rough idle for a few seconds can be normal after intake work.
• Listen for hissing (vacuum leak) and look for a check engine light.
• Take a short test drive, then recheck that the intake clamp(s) are tight and nothing is loose.
• If you get a check engine light or misfire, recheck coil connectors and any vacuum/EVAP hoses on the plenum.

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💰 DIY vs Shop Cost

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

DIY Cost: $80-$220 (parts only)

You Save: $230-$770 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?

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