🔧 RX350 - Spark Plug Replacement

On your RX350, replacing spark plugs restores strong ignition, smooth idle, and good fuel economy. The front three plugs are straightforward; the rear three usually require removing the cowl area and the upper intake manifold (the top part of the intake).

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

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⚠️ Safety & Precautions

• 🧯 Work on a fully cool engine to avoid burns and damaged threads.
• 🔋 Disconnect the negative battery terminal to prevent accidental shorting while unplugging coils.
• 🧼 Keep dirt out of the engine—do not let debris fall into spark plug holes.
• ⚠️ Do not use anti-seize on modern plated spark plug threads unless the plug maker specifically calls for it.
• 👀 Wear eye protection when using compressed air or brushing debris.

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🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Nitrile gloves
• Fender cover
• Floor jack (rated 3-ton minimum)
• Jack stands (rated 3-ton minimum)
• Wheel chocks
• 10mm socket
• 14mm socket
• 3/8" ratchet
• 1/4" ratchet
• 3/8" torque wrench (10–60 Nm range)
• 1/4" torque wrench (2–20 Nm range)
• 3/8" extension set (3", 6", 10")
• 3/8" wobble extension
• 14mm thin-wall spark plug socket (3/8" drive)
• Trim clip removal tool
• Flat-blade screwdriver
• Needle-nose pliers
• Small pick tool
• Shop vacuum
• Compressed air blow gun
• Painter’s tape and marker
• Flashlight
• Magnetic pickup tool

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

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

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📋 Before You Begin

• 🅿️ Park on level ground, shift to Park, and set the parking brake.
• 🔋 Use a 10mm socket to disconnect the negative battery terminal and isolate it so it can’t spring back.
• 🧽 Use a shop vacuum to clean loose dirt around the top of the engine.
• 🏷️ Use painter’s tape and marker to label any hoses/connectors you unplug (helps first-time DIYers).

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the engine cover

• Pull the cover upward by hand to release the rubber grommets.

Step 2: Replace the front bank spark plugs (easiest 3)

• Unplug each ignition coil electrical connector by lifting the lock with a small pick tool, then pulling the connector straight off.
• Remove each coil hold-down bolt using a 10mm socket.
• Twist the coil boot slightly, then pull the coil straight up and out.
• Blow out each spark plug well using compressed air blow gun so debris doesn’t fall into the cylinder.
• Remove the spark plug using a 14mm thin-wall spark plug socket with a 3/8" extension and 3/8" ratchet.
• Install the new spark plug by hand first using the spark plug socket and extension (no ratchet) until it seats. Hand-starting prevents cross-threading.
• Tighten the spark plug with a 3/8" torque wrench: Torque to 18 Nm (13 ft-lbs).
• Apply a very small amount of dielectric grease inside the coil boot (a pea-sized dab).
• Reinstall the ignition coil and tighten the hold-down bolt using a 1/4" torque wrench: Torque to 9 Nm (80 in-lbs).
• Reconnect the coil electrical connector (push until it clicks).

Step 3: Make room for the rear bank (cowl area access)

• Remove the wiper arm nuts using a 14mm socket.
• Wiggle the wiper arms off the splines by hand (use gentle rocking; do not pry on the glass with a tool).
• Remove the plastic cowl clips using a trim clip removal tool, then remove the cowl panels by hand.
• If any clips are stubborn, use a flat-blade screwdriver to lift the center pin, then pull the clip out.

Step 4: Remove the air inlet ducting and disconnect the throttle body area

• Loosen duct clamps using a flat-blade screwdriver, then remove the intake ducting by hand.
• Unplug any intake/throttle related connectors by releasing locks with a small pick tool and pulling straight off.
• Label hoses/connectors using painter’s tape and marker so they go back correctly.

Step 5: Remove the upper intake manifold (to reach the rear 3 plugs)

• Remove the upper intake manifold fasteners using a 10mm socket and 3/8" ratchet.
• Carefully lift the upper intake manifold up and off by hand.
• Cover the lower intake openings immediately using clean shop towels (prevents dropping anything into the engine).
• Remove old intake gaskets by hand and install the new gaskets (they should sit flat in their grooves).
• Reinstall the upper intake manifold fasteners with a 1/4" torque wrench: Torque to 21 Nm (15 ft-lbs).

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

• Repeat the same coil removal steps using a 10mm socket (unplug connector, remove bolt, pull coil).
• Blow out plug wells using the compressed air blow gun.
• Remove each plug using the 14mm thin-wall spark plug socket, 3/8" wobble extension, and 3/8" ratchet.
• Install each new plug by hand first, then torque with a 3/8" torque wrench: Torque to 18 Nm (13 ft-lbs).
• Reinstall coils and torque coil bolts with a 1/4" torque wrench: Torque to 9 Nm (80 in-lbs).

Step 7: Reassemble intake ducting and cowl parts

• Reinstall intake ducting and tighten clamps using a flat-blade screwdriver.
• Reconnect every electrical connector (listen/feel for a click).
• Reinstall the cowl panels and clips using a trim clip removal tool (press clips in squarely).
• Reinstall wiper arms and tighten nuts using a 14mm socket.
• Reinstall the engine cover by pressing it down by hand onto its grommets.

Step 8: Reconnect the battery

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

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✅ After Repair

• 🔎 Start the engine and let it idle for 1–2 minutes. It should run smooth with no shaking.
• 🧠 If the idle is rough, shut it off and re-check every coil connector and vacuum hose you touched.
• 👃 Listen for hissing (vacuum leak) around the intake manifold area.
• 🚗 Take a short test drive, then re-check for any warning lights.

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💰 DIY vs Shop Cost

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

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

You Save: $370-$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.