Lexus SC (1991-2000) SC 300 Spark Plug DIY

Replace the Spark Plugs on a Lexus SC 300 (1991-2000)

Works For:
1991 Lexus SC 300
1992 Lexus SC 300
1993 Lexus SC 300
1994 Lexus SC 300
1995 Lexus SC 300
1996 Lexus SC 300
1997 Lexus SC 300
1998 Lexus SC 300
1999 Lexus SC 300
2000 Lexus SC 300

Source: ClubLexus

Hey Everybody –

Got my SC Wednesday, so it’s time for a tuneup, as usual . First order of business is to change the plugs – lord knows how old they are/were.

I gotta say that changing the plugs on an SC300 is much harder than an RX-7 – on a ‘7 you just roll up with a spark plug socket and a socket wrench, pop the plug wires off, and change ’em. On the SC, there’s stuff in the way .

1. Remove the intake hose from the airflow meter to the throttle body. The stock hose clamps are Phillips head, but the “nut” is 10mm – use a 10mm ratchet, much easier and less chance of stripping the screw head. There’s also 2 vacuum lines – a large one in the back, and a short one in the front, both with spring clamps. Slide the clamp back, remove the vacuum lines, remove the intake hose. Again, you don’t have to remove the airbox or airflow meter at all.

2. Time for the throttle body. There are 2 electrical connectors – the ISC (idle speed control) and the TPS (throttle position sensor) – simply unplug and remove. You can use a flat head screwdriver between the plug and the body of the sensor to aid removal – push on the “button” on the connector, put the flathead there, and twist it a bit to help remove it. The “button” on my ISC connector disintegrated when I pushed it, due to it baking in the heat off the exhaust manifold. Since it’s a weatherpak connector, it’s a snug fit without the button – time will tell if this is a problem.

3. There are a total of 4 small vacuum lines to be removed – 3 on the top (they’re labeled with letters cast into the TB) and one on the side. The one on the side is easier to remove from the intake manifold end than the TB end, BTW. You’ll need needle nose pliers to break the hoses free. Two of mine tore, so I went ahead and replaced most of the hoses with some spare silicone vacuum hose from the RX-7.

4. Coolant lines. There are 2 lines going to the throttle body – the first is just to the left of the TB opening when looking from the passenger side. Pull the spring clip back, break the hose loose, and pull off – mine came off pretty easily. The second one is BURIED where it connects to the TB – I seriously doubt you could remove that one! I followed the hose around, and it connects to the water neck at the front of the engine. From the driver’s side, it’s not too bad to get to – again, move back the spring clip, break the hose lose, and remove. You don’t need to drain coolant or anything – coolant loss from these hoses is minimal at worst.

5. Throttle cables. There are 2 cables – one from the cruise control, one from the gas pedal. Use a 12mm crescent wrench to break the nut free that holds it in place, back the nut off a bit, and remove the cable from the mount. To remove the end of the cable that connects to the TB linkage, you may need to manually open the throttle, hold it open, and slip the cable off the end. Tuck those two out of the way.

6. Brackets and bolts. There is a square steel bracket under the entrance to the TB that has the O2 sensor plug clipped to it. It’s held on with 4 12mm nuts – remove. With that gone, look under the TB’s entrance – there are 2 more 12mm nuts hidden a bit. Remove those. At the top of the TB are 2 12mm bolts that are quite long – remove those. At this point, the TB should be free – it should flop around. If it’s stuck, something’s probably still bolted on, or some dumbass used RTV on the gasket . There’s a stamped metal gasket between the TB and intake manifold, BTW. Anyhow, remove the TB, feeding the coolant hose up through the intake manifold.

7. Engine cover. Now with the hard part done, time for the engine cover. Get a 5mm allen head wrench and remove the 6 chrome allen head bolts holding it on. Remove the oil fill cap as well, and remove the front engine cover. Put the oil cap back on to keep something from falling in the engine. The back cover is held on with 4 more 5mm allen head bolts – it should come off easily.

8. Plug wires/plugs. You may have to remove the plug wires in an odd order to deal with the clips that hold the plug wires in place, and getting around the intake manifold. I was able to remove all the wires and get to all the plugs without loosening or messing with the intake manifold at all – #3 and #4 are a little tricky for plug wire removal, but not bad. Get a good plug socket that has a rubber insert that grips the plug, break the plug loose, and remove. Reinstall the new plug with a light coat of anti-sieze on the threads, and tighten to a snug, NOT tight, fit. I usually put my hand at the head of the ratchet and tighten fully – that keeps you from using the ratchet’s leverage so they’re not too tight. Make sure to keep track of which wire goes to what plug (actually pretty idiot proof) and put the wires back in the clips – keeping the wires up and separate helps reduce crosstalk from the wires.

That’s pretty much it – took me around 2-3 hours to do, and it was my first time. I can probably do it in half the time next go-round. Assembly is the reverse .

A few notes –

– The TB to manifold gasket is stamped metal, and is typically infinitely reusable. DO NOT use RTV on that gasket – it doesn’t need it, and can actually CAUSE a leak moreso than fix one.

– If you are in the mood to do so, I highly recommend upgrading to silicone vacuum lines. RX-7 guys love them – they don’t cook into place like rubber, they look good, and they’re far more durable and heat resistant. is the ONLY place to get them from – the 3.5mm size is just right for the small lines. Hose Techniques uses thick-wall lines that won’t kink closed in a tight radius turn, they offer 3.5mm size (that fits nice and tight), and they’re quite reasonably priced and come in a range of colors. I used red, since that’s what I had in stock .

– When tightening the hose clamps for the TB inlet tube back up, use a 10mm socket/ratchet, or even better a 10mm nut driver. Put your hand on the head of the ratchet when tightening, and get them nice and snug, not too tight. If they strip/pop, get new hose clamps when you get the chance.

As usual, this is a great time to install new wires, cap, and rotor. I just wanted to get some new plugs on the car, as I was getting some mild hiccups in the powerband, which this helped. I used Bosch Platinum +2’s, which are decent plugs – next time I’d likely use NGK’s or Denso Iridiums.

Anyhow, and comments/corrections will be appreciated.


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