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Idle and driveability issues result from carbon buildup inside these pathways.
PCV system blowby may be a contributing factor.
Noticed another 2000 LS400 throttle body lid with the same deposits coinciding with inlet holes made me wonder whether the plate should be reconfigured..
(Image courtesy of Yamae) Carbon stalagmites depicted on inner area of cover plate.
A cover plate with a domed underside may solve this.
Perhaps a plate with a domed underside will be more conducive to airflow and reduce turbulence or dead spots and improve function of this critical intake junction.
Am fabricating a 1/4" thick Aluminum plate machined with domed underside to match inner perimeter of gasket.
is there an EGR system on the 98-00 engines? that carbon looks almost like it came from the exhaust. iirc, there is no EGR system on the newer 1UZs.
from the link:
The air mix path is designed to supply the air to injectors aiming to get better gas mileage mixing the gas and the air at the injector. This path is very important both for the mileage and the smooth acceleration.
Yamae;
Observed small diameter vacuum hose at top of image
This is different from North American LS400...which is plugged..
Where does it lead?
Your USDM LS400s lead it to the evaporation control system but JDM Celsior is plugged due the reason that the regulation is quite different.
It is all written in Japanese but see the page 20. I just pick up a part of the limit. The top horizontal line indicates countries. From left to right, California, USA, Korea, EU, Japan, Peking, China and Brazil. The vertical column indicates hours rate.
Your USDM LS400s lead it to the evaporation control system but JDM Celsior is plugged due the reason that the regulation is quite different.
It is all written in Japanese but see the page 20. I just pick up a part of the limit. The top horizontal line indicates countries. From left to right, California, USA, Korea, EU, Japan, Peking, China and Brazil. The vertical column indicates hours rate.
Anyone with color images.( vs Toyota parts diagram) of JDM Celsior system?
First article (rough) prototype of an Aluminum.air mix path cover plate depicting concept of domed underside to allow smoother transition of air at critical air mix path junction. Used 1/4" thick Aluminum plate. The profile will still.allow use of M5 x 0.8mm X 10 phillips panhead screws, but will order longer 16mm screws and cut back to 14mm length (or go with slightly thicker plate.and use off the shelf screws) Yard pull pull throttle body depicting clogged air mix path holes. The larger left and right air mix path holes route air through intake manifold passages to respective left and right fuel injector banks, while smaller holes conduit through to main throttle body inlet to control supply air Series of smaller air mix through-holes from air inlet mix cavity are visible slight-lower right at throttle blade and housing. This throttle body does not appear that it was ever cleaned.
This air mix path also exists on the SC430's engine. Ran into this gem of a thread while working out a small negative Long Term Fuel Trim on bank 1 that occurs mainly during idle and essentially disappears with wider throttle. When I cleaned my throttle body, I cleaned those little holes and two larger holes without understanding their function. Now it finally makes sense. Those little holes supply air for the fuel injectors' air mix paths. I'm thinking the air mix path fractional contribution to total air input diminishes as RPM's increase. That would be consistent with my low LTFT's on bank 1 going away a higher RPM.
Cleaning the air mix paths with CRC throttle body cleaner helped diminish the negative LTFT from -7-8% range to about half that. However, I only had half a can handy. I'm going to clean with more. If that doesn't fix it, then it's time to pull the injectors and see if there is a leaky one. Rather doubt that is the issue because engine is never difficult to start even if left standing over a few days.
Given that carbon buildup inside the air passages to the injectors is difficult to clean out, might letting the carbon preferentially build up in the air mix chamber be more beneficial than preventing it from building up in the chamber as a "trap?"
At any rate, thanks for putting up this thread. It's a well hidden detail of the engine.
Last edited by Seattle SCone; 02-25-21 at 01:59 AM.
Slight necro, but for the plate gasket; since it's NLA, has anyone tried sealing the plate with a careful application of RTV? I want to tackle this on mine, but I have a slight feeling my gasket is going to disintegrate upon removal, and I do have a bunch of Toyota FIPG left over from other jobs.
Slight necro, but for the plate gasket; since it's NLA, has anyone tried sealing the plate with a careful application of RTV? I want to tackle this on mine, but I have a slight feeling my gasket is going to disintegrate upon removal, and I do have a bunch of Toyota FIPG left over from other jobs.
Toyota FIPG was just fine in my case. I used it a few years ago to aid the original gasket which was partially damaged. So I used both the original gasket and the FIPG some to prevent the air leak.
I have cleaned the air mix passages on the throttle body of my 99, TB butterfly is spotless. Every vacuum hose is new, air filter clean, new spark plugs, new fuel filter. I still deal with the "low idle". (around 400rpm when fully warmed up with no loads, IE-AC or lights on). Never had an issue starting after sitting for even a month, fires right up and idles smooth. Only thing I haven't done is remove the intake and manually clean out the air mix passages. Would likely have the injectors sent out and cleaned/balanced during that job. I only drive the car 3k miles a year so not a big deal.
07-09-20, 02:43 PM
1998 1999 2000 ls400 throttle body air mix path cover plate
