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1998 Ls400 Throttle Body Removal And Cleaning


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Well, since I have a major portion of my engine disassembled, I have decided to clean my throttle body. The car is a 1998 LS400 with 118,000 and the throttle body has never been cleaned and the gasket is still the original. I've cleaned many a throttle body before and have never really noticed much change in the way a car runs after a cleaning. However, if a throttle body is literally caked on with carbon and oil, then that will affect a number of things, including throttle response, idle, acceleration, etc. Sometimes, the carbon can be so thick that the throttle plate has a tough time moving and/or moving smoothly. This job is fairly easy but will take a few hours (most of it spent cleaning the throttle body itself). I had it fairly easy as I have most of the stuff off due to my timing belt change and so had a straight and easy shot at the throttle body. Since I have not seen a thorough DIY on the board (correct me if I'm wrong), I've decided to add some good to the LS400 world so here it goes.

You will need a 12mm socket, a 45 degree long nose plier, a small flat nose plier, a new gasket (the old one can be reused and depends on the condition of the rubber seal), and a can of TB cleaner. It's best to remove the entire TB so that cleaning will be more thorough and easier.

1. Remove the V-Bank Cover (4 bolts), Air Cleaner Inlet, and Intake Air Connector. Disconnect the PCV Hose, EVAP Hose and PS Air Hose from the IAC.

2. Disconnect the Throttle Control Motor Connector, Throttle Position Sensor Connector and Accelerator Pedal Position Sensor Connector. Disconnect the accelerator cable by pushing the black round pedal thing up and sliding the cable end out of the hole.

3. Drain the coolant

4. Remove the No. 7 Water Bypass Hose that is under the Throttle Control Motor Connector.

5. Using a 12mm socket, remove the 2 nuts at the top and the 2 long bolts at the bottom from the TB.

6. Pull the TB towards the front. The only thing now holding the TB to the intake manifold is the No. 1 Water Bypass Hose located at the right side and behind the Throttle Control Motor. This is a tricky hose to get to as access is tight. It was easiest to remove the hose at the TCM connection using a 45 degree long nose plier to pry the clamp off of the hose. Set the clamp a few inches from the outlet to the right. Using a small plier, grab the hose and twist to break the seal. Then carefully pull the hose off.

7. Pull the TB completely off the studs.

8. Remove the gasket. Mine was still in pretty good shape. I'm sure I could have cleaned it up and reused it.

9. Proceed to clean the immediate inside and outside of the intake manifold. Mine had a bunch of mostly old oil and carbon junked on it. Cleans up nicely with TB cleaner. Don't overdo the cleaner. Spray a little where you want to clean and then immediately wipe off. The cleaner evaporates quickly so work accordingly.

10. Proceed to clean the TB. I stuck a screwdriver in the plate to keep it open. First spray and clean the general area. For the more caked on carbon, I took a small screwdriver and with the tip at an angle, scrubbed the carbon off. Don't scrub too hard as you don't want to gouge the inside. Clean the plate and make sure you get the edges of the plate also.

Presto, you're done, and you saved yourself a couple hundred bucks. With the money saved, you can enjoy about 20 six packs of beer, which is not too bad for a couple hours of work.

Installation is the reverse of removal.







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  • 5 weeks later...

May not seem like much... but I know when I cleaned the TB on my mom's 2001 LS430.... I had to disconnect the negative battery cable to reset the ECU as the car had very high RPMs at idle.... seems it has a learning component to it. Resetting the ECU allowed the idle RPM to return to normal. So while you may not think it makes a difference... the ECU thinks it does.

Thanks againf for another great tutorial with pics... excellent work.

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  • 11 months later...

Thanks richardkwon, I'm using all your tutorials. Valve gaskets, throttle body and the timing belt that landar started but you gave some great pointers in there too.

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  • 10 years later...

Has anyone tried this without emptying all the coolant out, just the radiator? I don't have the best ramps to get underneath the engine to drain the spigots by the O2 sensors.

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  • 2 weeks later...

Draining just the radiator should be sufficient.

You do know the proper procedure on how to refill and bleed the cooling system?

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