Here’s a step by step tutorial on how to replace the valve cover gaskets, spark plugs and spark plug wires on a Lexus GS300 or IS300 with the 3.0L inline 6 2JZ-GE engine.
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.
The procedure consists of first removing the engine covers and air intake tubes. A few electrical connectors and vacuum hoses must then be disconnected from the throttle body, along with the throttle cable. Be sure to label all connectors and hoses that have been removed for easier reassembly. The intake and throttle body is then removed as one assembly.
The use of a ratcheting wrench is recommended when accessing intake plenum bolts.
Once the intake is out of the way, the wiring harness must be freed from both sides of the valve cover and the ignition coil pack connectors removed. Usually the coil pack connectors have a tendency to break and should be replaced if they do. The wiring harness is also very brittle from the engine heat cycling over time.
Next, the ignition coil and wires can be removed. Make sure the spark plug tubes and area between the covers has been thoroughly cleaned before unbolting the 6 10mm bolts and 2 10mm nuts holding each valve cover on.
Wiggle the valve cover to break it free and work it around the engine harness and heater core hose. Clean all mating surfaces with brake cleaner and a lint free rag.
A Fel-Pro gasket was used to reseal the valve covers. For some reason it came with two driver side gasket and one passenger side gasket. Permatex black RTV was used around the “half moon” cam profile of the valve cover to aid the gaskets in sealing the corners.
The ignition wiring harness was then swapped over to a new one from NGK, and the spark plugs were changed for fresh new Denso double electrode plugs. It is important that double electrode plugs be used since this engine uses waste spark ignition, which means three coils power six cylinders.
Once the spark plugs, ignition coils and wires have been replaced, the intake system can then be cleaned using throttle body cleaner and then reinstalled onto the car. There are a number of vacuum hoses under the intake plenum that may take a while to reconnect.
A new plenum to throttle body gasket was used. Reinstall the plenum nuts and bolts, as well as the throttle body bracket on the passenger side of the engine, reconnect the coolant lines and electrical connectors.
Start the engine and let it warm up. Degrease the engine if it is oily and dirty, and take it for a long drive, stopping periodically to check for leaks.
The car will now run smoother and more responsive with the new plugs and wires, and won’t leak and burn oil.
Here’s the full write-up and discussion: