Valve Cover and Spark Plug Replacement

Here's how to replace the valve cover gaskets, spark plugs and wires on a Lexus GS300 and IS300.

Here's a short video on the procedure:

Leaking valve cover gaskets are a common problem as vehicles age. On this Lexus GS300, the valve cover gaskets were leaking so badly that the spark plug wells were filled with oil and gunk.

Since the intake and throttle body have to be removed to do this job, it is also recommended to change the spark plugs and spark plug wires while they are easily accessible.

Changing the spark plugs will make the vehicle run smoother, be more responsive and efficient. Fixing the valve cover gasket leak will stop oil loss and reduce the smell as oil burns against the exhaust.

Step 1: Remove the Engine Cover

The valve covers are located under the engine covers and intake. Start by removing the covers, and then the intake tube before the throttle body.

Step 2: Disconnect Hoses and Electrical Connectors

The throttle body and part of the intake will have to be removed to access the valve covers and spark plugs underneath.

There are a number of vacuum hoses, electrical connectors and coolant lines to be removed, including a small green vacuum switch behind the intake that's held on by a bolt.

The front coolant line can be removed now, and the rear coolant line will be removed once the throttle body is unbolted.

Step 3: Unbolt the Throttle Body

There are 4 bolts and 2 nuts that hold the intake to the plenum on the drivers side of the car, and two additional 12mm nuts on the passenger side.

The use of a ratcheting wrench is helpful for accessing those nuts under the intake.

Step 4: Remove the Ignition Wires and Coils

Remove the ignition harness from the coils. Be-careful as they're brittle and will break and you'll need to replace them.

Here you can see how much oil was built up in the spark plug wells due to the leaking valve cover.

Next start unbolting the valve cover, each one has 6 10mm bolts and two 10mm nuts on studs.

Step 5: Under the Valve Cover

Here's what it looks like under the valve cover. This engine hasn't been that well maintained and there is some sludge buildup.

Its also a good time to clean out or change the PCV valve.

Use some engine degreaser to clean up the valve covers.

Step 6: Take a Break

Take a 5 minute nap in the midday sun. Half the job is done, time to put things back together.

Step 7: Replace the Valve Cover

A Fel-Pro gasket kit was used to replace the valve cover gaskets.

Use some Permatex RTV on the corners of the half-moon shaped parts of the valve cover where it goes over the cam to help it seal better.

Torque down the valve cover gasket bolts to 75 in-lb.

Step 8: Replace the Spark Plug

Using a spark plug socket, unscrew the old spark plug and replace them with new ones!

Denso dual electrode spark plugs were used for this engine, since it has waste spark ignition.

Step 9: Change the Coil Pack Connectors

Remember those brittle coil pack connectors? Now's a good time to change them.

They can be found on eBay. You should buy 3 in case all three of them break. In this case only the front one disintegrated. A pin was used to de-pin them from their contacts and the new one slides right in.

Step 10: Change the Ignition Wires

An NGK spark plug wire set (blue) was used to replace the original wire set, which was getting hard and brittle.

The brackets were transferred over, and they were plugged into the new coils.

The coils and wires were then installed back into the car, and tidied up - getting ready for the intake to go back on.

Step 11: Replace the Intake

Before replacing the intake, its a good idea to run some carb cleaner down the plenum and theback of the throttle body and clean it up with an old tooth brush. The PCV system in the car always makes the throttle body and intake gummed up with oily deposits that need to be cleared our periodically. So why not clean it now while its off the car?

When completed, reinstall the intake onto the car, using a new throttle body gasket.

Step 12: Replace Vacuum Hoses and Electrical Connectors

This is where labeling the connectors and hoses come in handy when you were taking things apart.

Double and triple check that everything is connected before starting the car.

Step 13: Start It Up!

You should be good now to start up the car and make sure it runs properly.

If its hard to start, its probably the throttle body cleaner offsetting the fuel mixture and it will burn off.

The car should run smoother now, with new spark plug and wires, you might even notice the throttle more responsive. Furthermore there should be no more leaks, which means no more mess on the driveway or burning oil smell as it drips on the exhaust.