Guides  /  2010 Lexus RX350

2010 Lexus RX350 Spark Plug & Ignition Coil Replacement (Step-by-Step)

A 2010 Lexus RX350 hits its 120,000-mile service with a long maintenance list, and spark plugs and ignition coils are near the top. A dealer will happily charge you several hundred dollars for the labor alone — most of that is the awkward access to the rear bank of cylinders. Do it yourself and you’re only paying for parts.

Fair warning: this is the hardest of the common RX350 DIY jobs. The front three cylinders are a breeze. The back three live under the intake at the very rear of the engine bay, so plan on some time leaning over the fender. The creator rates it a 4 out of 5 and spent three to four hours on it. Here’s the full sequence.

Before you start

Do this whole job with the engine cold. The coils sit right on top of the plugs on the front bank; the other three are buried under the intake. Lay out your new coils and plugs, and grab a 5mm hex key in case you decide to pull the intake.

Part 1 — The easy front three

1. Unhook the coil connectors on the front bank.
2. Remove the coil pack bolts with a 10mm socket — they should be fairly loose. Pull the coils out and check the wells for oil. Seeing no oil down there is a good sign (oil means leaking valve cover seals).
3. Blow out the wells with compressed air before you unscrew anything, so no dirt drops into the cylinder when the plug comes out.
4. Break the plugs loose. Use the magnetic swivel-head spark plug socket on a 3/8” ratchet. The old plugs can be seized in tight — a length of pipe (the creator used a bicycle seat post) slipped over the ratchet handle gives the leverage to crack them free. The magnet holds the plug as you lift it out.
5. Install the new plugs to about 12 lb-ft — just past finger tight. Don’t over-torque them.
6. Refit the new coils, bolt them down with the 10mm, and reconnect the plugs.

Pro tip: while you’re in here, the PCV valve is right there (19mm). It’s cheap and easy to swap at the same time — the creator did his as a matter of course.

Part 2 — Getting to the rear three

This is where the time goes. The rear plugs are hidden under the intake at the back of the engine, so you have to clear a path.

1. Remove the cowl piece. Release the spring tension and it lifts off — note how it aligns so you can put it back. It’s held by a lot of small clips, so expect a bit of a fight on reassembly.
2. Unbolt the windshield wiper assembly (bolts on each side) and set it aside.
3. Remove the cowl tray. The bolts along the back of the tray double as part of the strut mount — one is outside, two are inside. The firewall behind it stays put. Once those back bolts are out, the tray lifts free (you have to work it over the threads).
4. Remove the bracket over the rear coils — there are two bolts underneath it.
5. Disconnect the rear coil/plug wiring, noting where each connector goes so you can reassemble it. There are a lot of wires and hoses back here; it’s easy to forget routing, so take photos as you go.

Part 3 — Pull the intake (recommended) and swap the rear plugs

The intake is held by just two bolts to the head. You can reach a couple of the rear coils without removing it, but the creator pulls the intake — the rear space is so tight you end up cramming and gouging your arm otherwise.

1. Remove the two intake bolts and lift the intake off.
2. Swap the rear three coils and plugs exactly as you did the front: blow out the wells, break the plugs loose, install new plugs to ~12 lb-ft, fit the new coils.
3. Reassemble in reverse — intake, wiring, bracket, cowl tray, wiper assembly, cowl piece. Re-route every connector the way it came off.

Fire it up

Turn the key to ON first, then start it. No check-engine light and a quiet, smooth idle means you’re done. It’s a long job — your back will feel it — but once you’ve seen it laid out, it’s well within reach of a confident DIYer, and you’ve saved the dealer’s labor bill on a 120k-mile must-do.