Replacing the Spark Plugs in your Lexus IS

Overview

A rough idle, misfires and a sluggish throttle response are symptoms of a bad or dying spark plug. They're one of the few engine components that are exposed to combustion, so they're pretty rugged. Still, Lexus recommends you change them every 60K miles. However, they can fail earlier and trigger a check engine light. Luckily, changing the plugs yourself isn't all that difficult.

Time: 2 Hours

DIY Cost: $90

Pro Cost: $280

Difficulty: Easy/Moderate

Materials Needed

• New spark plugs
• 10mm socket with extensions
• Spark plug socket tool or a 16mm deep socket or 5/8 deep socket
• Torque wrench
• Flat head screwdriver (for prying)
• Ratcheting wrench or box wrench

Step 1 - Remove engine covers and air intake assembly

Pop off the panels and remove the air intake assembly. You can see that the ignition coil is now easily exposed.

Figure 1. Remove this intake tube according to diagram

Figure 2. The finger in this image points to an ignition coil. Underneath it is a spark plug.

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Step 2 - Loosen ignition coil harness

Using a small socket or wrench, loosen the 10mm nuts holding the harness in place.

Figure 3. You don't need to remove the harness, but loosening the bolts will give you some wiggle room when pulling the coil packs.

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Step 3 - Remove fastening nuts from ignition coils and unclip coils

Remove the 10mm nuts holding the ignition coils in place. Save the nuts and set aside on a magnetic tray or a cup.

Figure 4. Remove the ignition coil bolt from the coil pack.

Figure 5. Unclip the ignition coil from the wiring harness.

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Step 4 - Remove old spark plug

The old spark plug will now be exposed. Use the spark plug tool with an extension to remove the old plug.

Figure 6. The spark plug sits deep in the engine. You'll need an extended socket to reach it.

Figure 7. Fit the extension and socket on the spark plug loosely before wrenching.

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Step 4 - Continued

Now that your have your spark plug out, you can check its condition to see if your engine is having problems. A spark plug can tell you a lot about what's happening in your combustion chamber if you know how to read it. Compare your plugs to ones on this chart. If your engine is running poorly, this will help you figure out why.

Figure 8. Common spark plug wear patterns.

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Step 5 - Install new spark plug

Using the spark plug tool and the extension, guide the new plug into the hole and thread loosely. 

Pro Tip:

You can apply a small amount of motor oil to the threads of the new spark plug to avoid cross threading.

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Step 6 - Torque down the spark plug

Using the torque wrench, set it to 18 ft-lb and tighten.

Figure 9. Tighten the spark plug using the torque wrench.

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Step 7 - Remove ignition harness on driver's side

Navigate to the driver's side and remove the two nuts shown in Figure 10. After they've been removed, lift the harness up and off to the side. Save and set the nuts aside.

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Step 8 - Replace spark plugs on driver's side

Repeat Steps 3-6 on the driver's side of the engine. Don't forget to torque new plugs down!

Pro Tip:

Since the driver's side of the engine is a much tighter fit, a box wrench or ratcheting wrench will be the most useful here.

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Step 9 - Re-install nuts, air intake asssemby, and engine covers

Re-install the fastening nuts for the ignition coils and the harnesses. You should also reinstall the air intake assembly and engine covers at this time.

Featured Video: How to Replace Spark Plugs.

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For help with your do-it-yourself maintenance and repair projects, please visit our how-to section in the forum.