Changing a spark plug in a Lexus IS 300 is not as simple as finding the plugs, taking the old ones out and putting new ones in. Because of the engine design of the car, you'll have to take apart and move much of the throttle body before spark plugs can be replaced. You'll need a thorough knowledge of cars, engines, tools and terminology to complete this task in minimal time.
Park your car in a cool, well ventilated space and allow the car (the engine, specifically) to cool. Once cooled, open the hood and ensure that you have enough light. Use a snake light or simple flashlight if you need more light.
Unscrew the four 10mm acorn nuts holding the engine cover onto your throttle body. You'll need a 10mm socket wrench to do this.
Remove the four screws located on the timing belt cover. These are 5mm allen key screws and must be removed with your 5mm allen wrench.
Locate the intake tube/resonator next to the recently removed engine cover. On it are two hose clamps that are closed with a 10mm bolt. Remove the bolts from both ends of the tube and press the clamps together. You may have to wiggle the apparatus, but it should pop off its location fairly easily. Take the tube out of the car and set it aside.
Remove the three sensors (the accelerator pedal sensor, throttle position sensor, throttle control sensor) from their locations. You should be able to just pop out of their locations using your fingers. You can use a screwdriver if necessary.
Rotate the throttle cable spool so that there is slack in the line. Once there is ample slack, remove the cable from its positioning in the throttle body.
Use your 12mm socket wrench to undo the nuts that hold the engine wire clamp in place. There should be four, and they should be tight. But once loosened, they should be easily removed. Then remove the wire clamp from the engine.
Unscrew the three 12mm bolts from the throttle body. There will be two on top that extend the entire way from the front of the throttle to the back throttle gasket. There is also one on the bottom, immediately under the intake butterfly. Removing the bolts will allow the throttle body to be moved slightly out of the place (leave the hoses intact). Move it toward the passenger side of the car, exposing the throttle gasket.
Remove the throttle gasket from its positioning by using your 12mm socket wrench to remove the three bolts holding the gasket in place. There should be two on top, and one on the bottom. Remove the bolts and then remove the gasket.
Locate the three coils below the throttle gasket and throttle body that you just moved out of the way. Connected to each of these coils is an engine harness--pull up on the coil to undo the harness, which should disconnect easily from the engine.
Unscrew the two 10mm bolts that hold the wire guides in place.
Remove the plug wires from the coil below it by pulling the plugs up and away from the coils--bypassing the locking plug/high tension harness. You should be able to easily remove this with the right force in the same way that the harnesses were disconnected in step 10--don't force it!
Remove any wires still connected to the throttle body--this includes high tension wires and plug wires and wire guages. Disconnect them and move the throttle body away, exposing the spark plug channel below it.
Remove the plug wires and coils from the spark plug channel. They need to go back onto the new spark plugs in the exact same order, however, so be sure to keep your parts organized. Removing all of the wires and coils will now expose the six spark plugs themselves.
Remove the old plugs and clear any dirt or debris in the channel before inserting new spark plugs. Use a rag or vacuum if necessary. Insert the spark plugs gently, being sure not to drop them in to avoid bending the electrodes at the bottom. Once they are in place, turn them counter-clockwise until you hear/feel a click, and once you do, turn them clockwise by hand. When you can no longer tighten by hand, use a ratchet to finish the job. Tighten them to 13 ft. lbs.
To put everything back in order, follow these instructions in reverse-- starting by inserting the plug wires and coils into the spark channel (where you meticulously ordered the wires so you didn't mix them up in step 14), all the way to screwing in the four acorn nuts on the engine body.
