🔧 ES350 - Spark Plug Replacement

On your ES350, 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 it to access them. Replacing all 6 plugs restores smooth idle, fuel economy, and prevents misfires.

Difficulty Level: Advanced | Estimated Time: 2.5-4.5 hours

Assumption: 3.5L V6 with 6 coil-on-plug ignition; rear bank requires plenum removal.

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⚠️ Safety & Precautions

• ⚠️ Work on a fully cool engine to avoid burns and stripped threads.
• ⚠️ Disconnect the negative battery cable before unplugging the throttle body and ignition coils.
• ⚠️ Keep dirt out of the intake—cover openings with a clean lint-free rag.
• ⚠️ Do not use anti-seize on these plugs; the threads are plated and anti-seize 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 torque wrench (10-30 Nm range)
• 5/8" spark plug socket
• 3/8" drive extension set (3", 6", 10")
• 3/8" drive wobble extension
• Flathead screwdriver
• Phillips screwdriver
• Hose clamp pliers
• Trim clip removal tool
• Compressed air blow gun
• Magnetic pickup tool
• Shop towels
• Fender cover

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Spark plugs (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 10mm socket to disconnect the negative battery terminal and isolate it so it can’t spring back.
• Lay out 6 spark plugs in order; replace one cylinder at a time to avoid mixing parts.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the engine cover

• Pull up on the plastic engine cover to release it from its rubber grommets (it’s press-fit).
• Set it aside where it won’t get stepped on.

Step 2: Remove the air intake ducting

• Use a flathead screwdriver to loosen the hose clamps on the intake tube.
• Unclip/unbolt any resonator brackets using a 10mm socket.
• Lift the intake tube/air duct out. Take a quick photo first.

Step 3: Replace the front bank (radiator-side) 3 spark plugs

• Unplug one ignition coil connector by pressing the tab and pulling straight back (no yanking).
• Use a 10mm socket to remove the ignition coil hold-down bolt.
• Pull the coil straight up and out (an ignition coil is the pencil-shaped part that sits on top of the plug).
• Blow out the spark plug well using compressed air blow gun so dirt can’t fall into the cylinder.
• Use a 5/8" spark plug socket, 3/8" ratchet, and a 6" extension to remove the spark plug.
• Install the new spark plug by hand first using the spark plug socket and extension (no ratchet yet) so it doesn’t cross-thread.
• Torque the spark plug: Torque to 18 Nm (13 ft-lbs).
• Apply a small smear of dielectric grease inside the coil boot (dielectric grease helps prevent moisture/arching).
• Reinstall the coil and bolt: Torque to 10 Nm (89 in-lbs).
• Plug the coil connector back in until it clicks, then repeat for the other 2 front cylinders.

Step 4: Remove components to access the upper intake manifold

• Disconnect any vacuum hoses and electrical connectors attached to the upper intake manifold using your hands and a flathead screwdriver as needed.
• Remove brackets/bolts in your way using a 10mm socket and 12mm socket.
• Use hose clamp pliers to release spring clamps on small hoses (pinch, slide back, then twist hose gently to break it loose).
• If you remove plastic push-clips, use a trim clip removal tool to avoid breaking them.

Step 5: Remove the throttle body from the intake (set aside, don’t stress hoses)

• Unplug the throttle body connector by pressing the tab and pulling straight off.
• Use a 10mm socket to remove the throttle body mounting bolts.
• Carefully move the throttle body aside and support it with a towel; do not kink any hoses.
• Remove and discard the old gasket; install the new one during reassembly.
• Reinstall throttle body later: Torque to 8 Nm (71 in-lbs).

Step 6: Remove the upper intake manifold (plenum)

• Use a 12mm socket (and extensions as needed) to remove the upper intake manifold bolts/nuts.
• Lift the plenum straight up and out. If it’s stuck, gently wiggle—do not pry hard on plastic.
• Immediately cover the lower intake openings with clean shop towels to prevent anything from falling in.
• Remove and discard the old upper intake manifold gaskets; install new gaskets for reassembly.
• During reassembly, tighten the plenum evenly: Torque to 21 Nm (15 ft-lbs).

Step 7: Replace the rear bank (firewall-side) 3 spark plugs

• Repeat the same process as the front bank: unplug coil, remove coil bolt with 10mm socket, pull coil out.
• Blow out each plug well using compressed air blow gun.
• Remove each spark plug using 5/8" spark plug socket, wobble extension, and ratchet.
• Install new plug by hand first, then torque: Torque to 18 Nm (13 ft-lbs).
• Reinstall coil and bolt: Torque to 10 Nm (89 in-lbs).

Step 8: Reassemble the intake system

• Remove the shop towels from the intake ports (double-check nothing fell in).
• Install new upper intake manifold gaskets, then set the plenum back on.
• Start all plenum bolts/nuts by hand, then torque evenly: Torque to 21 Nm (15 ft-lbs).
• Install the throttle body with a new gasket and torque bolts: Torque to 8 Nm (71 in-lbs).
• Reconnect every vacuum hose and electrical connector until fully seated/clicked.
• Reinstall the intake ducting and tighten clamps with a flathead screwdriver.
• Reinstall the engine cover (press down to snap into grommets).

Step 9: Reconnect the battery

• Use a 10mm socket to reconnect the negative battery terminal snugly.

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✅ After Repair

• Start the engine and let it idle for 2-3 minutes; the idle may fluctuate briefly after throttle body unplugging.
• Listen for hissing (vacuum leak) around the intake; if heard, recheck clamps, hoses, and plenum seating.
• Road test 10-15 minutes, then recheck for any warning lights and recheck the intake tube clamps.
• If a check engine light appears, the most common causes are a loose connector or vacuum hose left off.

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💰 DIY vs Shop Cost

Shop Cost: $450-$900 (parts + labor)

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

You Save: $360-$680 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 2.5-4.5 hours.

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🎯 Ready to get started?

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