🔧 RX350 - Spark Plug Replacement

Your RX350 uses six long-life spark plugs (one per cylinder). Replacing them restores smooth idle, power, and fuel economy, and helps prevent misfires as mileage builds.

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

Assumption: 3.5L V6 requires upper intake removal for rear plugs.

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⚠️ Safety & Precautions

• ⚠️ Work on a fully cool engine to avoid burns and prevent thread damage in the aluminum heads.
• ⚠️ Disconnect the negative battery cable to prevent accidental short circuits while unplugging ignition coils.
• ⚠️ Keep dirt out of the engine: never leave intake ports open; cover them with clean rags immediately.
• ⚠️ Do not over-tighten spark plugs; stripped threads are an expensive repair.
• ⚠️ Use only the correct plug type (iridium, correct heat range and gap); do not “re-gap” fine-wire iridium plugs.

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🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Nitrile gloves
• 10mm socket
• 12mm socket
• 14mm socket
• 3/8" ratchet
• 3/8" torque wrench 5-80 Nm
• 1/4" torque wrench 2-20 Nm
• 3/8" extension set 3" to 10"
• 3/8" swivel adapter
• 14mm thin-wall spark plug socket
• Flat trim clip removal tool
• Needle-nose pliers
• Flathead screwdriver
• Magnetic pickup tool
• Compressed air blow gun
• Shop light
• Clean shop rags
• Painter’s tape and marker

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Iridium spark plugs - 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).
• Use painter’s tape and marker to label hoses/connectors as you remove them.
• Disconnect the battery: use a 10mm socket to remove the negative terminal and tuck it aside 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 and intake ducting

• Pull up to remove the engine cover (it’s held by grommets).
• Loosen intake hose clamps with a flathead screwdriver.
• Unclip/unbolt any intake snorkel pieces using a 10mm socket and remove the air ducting.

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

• Unplug each ignition coil connector by pressing the tab and pulling straight back.
• Remove each ignition coil hold-down bolt using a 10mm socket.
• Twist and pull the coil upward to remove it.
• Blow debris out of the spark plug well using a compressed air blow gun so dirt can’t fall into the cylinder.
• Remove the spark plug using a 14mm thin-wall spark plug socket, 3/8" ratchet, and 3/8" extension set 3" to 10".
• Install the new plug by hand first using the spark plug socket and extension (no ratchet yet) so it doesn’t cross-thread. Hand-threading prevents expensive damage.
• Tighten with a 3/8" torque wrench 5-80 Nm: Torque to 18 Nm (13 ft-lbs).
• Apply a tiny smear of dielectric grease inside the coil boot (it helps prevent moisture issues).
• Reinstall the coil and tighten the coil bolt: Torque to 10 Nm (89 in-lbs).
• Reconnect the coil electrical connector until it clicks.

Step 3: Gain access to the rear-bank spark plugs (intake removal)

• Disconnect electrical connectors around the throttle body and intake area (label them with painter’s tape and marker).
• Remove vacuum/PCV hoses using needle-nose pliers to slide clamps back, then twist hoses gently to free them.
• Remove the throttle body fasteners using a 10mm socket. Set the throttle body aside carefully (do not bend or strain coolant hoses if equipped).
• Remove the upper intake manifold fasteners using a 12mm socket and 3/8" ratchet.
• Lift the upper intake manifold straight up and off. If it sticks, tap gently by hand—do not pry hard on sealing surfaces.
• Immediately stuff clean shop rags into the exposed intake ports so nothing can fall in. One dropped bolt can ruin your day.

Step 4: Replace the rear-bank spark plugs

• Unplug the rear ignition coil connectors and remove coil bolts using a 10mm socket.
• Remove coils, then blow out each plug well using the compressed air blow gun.
• Remove spark plugs using the 14mm thin-wall spark plug socket, 3/8" extension set 3" to 10", and 3/8" swivel adapter as needed for angle.
• Install new plugs by hand first, then torque: Torque to 18 Nm (13 ft-lbs).
• Add a small amount of dielectric grease inside each coil boot, reinstall coils, and torque coil bolts: Torque to 10 Nm (89 in-lbs).
• Reconnect all coil connectors until they click.

Step 5: Reinstall the intake manifold and throttle body

• Remove the rags from the intake ports and count them to confirm none are left behind.
• Replace the intake gaskets with the new upper intake manifold gasket set.
• Set the upper intake manifold in place and start all fasteners by hand.
• Tighten intake fasteners evenly using a 12mm socket and then torque with a 3/8" torque wrench 5-80 Nm: Torque to 21 Nm (15 ft-lbs).
• Install the new throttle body gasket, reinstall the throttle body, and torque using a 10mm socket and 1/4" torque wrench 2-20 Nm: Torque to 10 Nm (89 in-lbs).
• Reconnect all hoses and electrical connectors you labeled. Double-check every clamp with needle-nose pliers as needed.

Step 6: Reinstall intake ducting and reconnect the battery

• Reinstall the air ducting and tighten clamps using a flathead screwdriver.
• Reinstall the engine cover by pushing it into the grommets.
• Reconnect the negative battery terminal using a 10mm socket.
• If you dropped hardware, use a magnetic pickup tool to retrieve it before starting.

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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 after battery disconnect.
• Listen for vacuum leaks (hissing). If you hear one, recheck intake hoses and that the intake manifold is seated.
• Road test for 10-15 minutes. Verify no check engine light and no hesitation under acceleration.
• Recheck for any loose tools or rags in the engine bay with a shop light.

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💰 DIY vs Shop Cost

Shop Cost: ₹12,000-₹25,000 (parts + labor)

DIY Cost: ₹3,500-₹9,500 (parts only)

You Save: ₹8,500-₹15,500 by doing it yourself!

Shop labor rates vary but typically run ₹800-₹2,000/hour. This repair takes a shop approximately 2.5-4.0 hours.

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🎯 Ready to get started?

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