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1998 LS400
305,000 miles
Shifting has been rough at low RPM lately.
Recently has stumbled and stalled at low rpm.
The engine has been very well maintained and has run smoothly through all ranges until this most recently .
The stumble and recovery seems as if the engine has trouble recognizing some signal at low RPM.
Any ideas ?
It has never let me down before.
Clean the Air Mix paths above the throttle body. Take the plastic intake piping out and then there will be a cover plate that you also have to remove directly above the throttle body behind it that has about 8 or 10 small holes that supply air to the cylinders. If these are blocked up with carbon it can cause similar symptoms with idle and driveability.
Thank you guys for the great ideas! I should have time for checking the items this weekend . If I decide to replace the maf, where do you recommend purchasing? Would this be an item you recommend getting from Toyota ? or would a good aftermarket unit be ok? Now that I think of it, Its really old and am reluctant to clean it .
Ok Toyota/lexus techs.
I bought a Lexus maf sensor, cleaned up the air intake and changed the air filter. The shifting and acceleration is smooth now.
But... The engine died again. Again on a steep hill. I tried restarting, the starter cranked it fast but no start. I was able to coast back down, turn it around pointed downhill, then it restarted and has run beautifully for miles since. Oh and Goldstar, there are no codes or check engine .
Symptoms I have recently noticed:
Engine shut down two different occasions on steep hills.
Dash lights briefly flickering
MPG computer reset the "miles on tank" back to zero before I refilled.
So tell me what you think. What connection point (or other potential issue) should I look at?
Thank you
Clean the Air Mix paths above the throttle body. Take the plastic intake piping out and then there will be a cover plate that you also have to remove directly above the throttle body behind it that has about 8 or 10 small holes that supply air to the cylinders. If these are blocked up with carbon it can cause similar symptoms with idle and driveability.
Do you know if the 92 ls 400 has an air mix path? I haven't been able to find where it is if there is one, and searching the forums hasn't helped in this pursuit. All I've seen is info on 98+ ls 400s (VVTi) having the air mix path.
The air-mix path feeds the fuel injectors, bypassing the throttle plate to run the system. The LS400 got air-assisted injectors in 1996... but then later in this document it says "without air assist". So I'm not sure.
The air-mix path feeds the fuel injectors, bypassing the throttle plate to run the system. The LS400 got air-assisted injectors in 1996... but then later in this document it says "without air assist". So I'm not sure.
Do you know if the 92 ls 400 has an air mix path? I haven't been able to find where it is if there is one, and searching the forums hasn't helped in this pursuit. All I've seen is info on 98+ ls 400s (VVTi) having the air mix path.
don't believe it does... the pre-1997 LS models still use a dedicated idle air control (IAC) valve at idle speeds since the throttle control was still entirely mechanical
1998 models have electronic throttle control with the throttle plate opening fully computer controlled, so they have an 'air mix path' in the absence of that IAC valve
Thank you forum members for the help!
Much better now that I:
Installed OEM maf.
Replaced air filter
Removed TB assy and carefully cleaned all the little holes under the little cover .
Cleaned TB and buttlerfly
Replaced TB gasket
Isolated the vacuum/vent lines to PS pump.
Cleaned PCV
Because of the sudden stalling, herky jerky shifting, flashing of dash lights (and what I think was the "miles traveled on tank" resetting) and the fact that I had cleaned the TB a couple years ago, I didn't want to believe the above would be the cause.
But I listened and took action. So smooth with higher idle now! I plan to order many new vacuum tubes and replace soon since I suspect they are not 100%.
Time will tell since the problem seemed to occur every 100 miles or so. But so far it's a sweet engine.
Seems like Toyota vacuum hose lasts longer than the ones you get at DIY places. And you only need one size. When I replaced the hoses on mine, I just bought the longest length and cut it to fit.
10-23-23, 08:52 AM
1998 with 305k. Stumble at low rpm, stalled once.
