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Noticed several postings concerning coggy upshifting and downshifting on 1998-2000 LS400's with A650-E transmission....
Aftee two decades and 160,000 miles of driving in a narrow RPM range, suggests the throttle position sensor as the culprit.(instead of Pedal Position sensor)
Transmission shifting was unLexus-like, ..especially on deceleration, yet no trouble codes..
The TPS is a mechanical device with a bearing and sliding contacts...with resulting wear over time ...and in a very narrow arc on the circuit board traces.
My TPS made an audible grinding noise so elected to replace... about $100 with tax for OEM Denso.
(If you use afterrmarket, then don't complain if it doesn't perform...just expect the worst.)
Noticeable improvement in shifting behavior with new Denso TPS...
Old OEM Denso Throttle Position Sensor with P.N. for ordering..
Well worth doing.
This probably would apply to any LS400 with125,000.+ miles....age-related oxidation is also a consideration.
ive never know that tps can affect transmission shifting.
Reporting my situation...your results may vary.
1999 LS400 does not use a dedicated cable from throttle body to transmission, so plausibly it is.directed electronically from ECU, based on sensors input;, including; Coolant temperature sensor, Throttle position sensor, Pedal position sensor, Knock sensors, Vehicle speed sensors, Acceleration sensors (?), Transmission temperature sensor, Brake pedal switch, etc...
The OEM sensors are quite durable
(as are the cars 20+ years...which explains why we see a car that still looks new and we discuss its age-relted issues here)
but they experience degradation through use and, or, time...
While no trouble code triggered for TPS, my sense was it was tired...In comparison to new sensor, the bearing was a bit wobbly and there was more pronounced audible intermal scraping noise of wiping contacts over conductive traces. ..especially in one areas of arc , probably corresponding with 1,500-2,000 RPM range.
After the Gas pedal.position sensor, one of the hardest working mechanical sensors.
The Gas Pedal Position Sensor is next on my list..howevet, .it is about 3X the cost...
20 years old and 160,000 miles time to change a few electromechanical components.
Good info YODA.
You might add a little info re how to calibrate the TPS as it's not a simple bolt on swap.
I'm familiar with the process, which requires a multimeter, but I'm no expert...
Good info YODA.
You might add a little info re how to calibrate the TPS as it's not a simple bolt on swap.
I'm familiar with the process, which requires a multimeter, but I'm no expert...
You will require an OBD Ii scan tool that displays TPS settings for initial 15 degrres indexxing of sensor....
Afterwards, when engine running, the sensor opening percentage reading should display between 10 - 14%...(Asked Lexus for clarification and they told me indexxing is not required... just bolt it in...@#$&*)
good work. did this fix your deceleration pulse issue on another thread?
It did not.
The Accelerator Postion sensor is also suspect...
For safety, it is configured to sense both directions of accelerator...so two sets of tracks...possibly the deceleration circuit traces/contact area has a void.or low spot..
Does not occur when gradually releasing the accelerator pedal from 2,200 RPM to idle.
Noticeable when quickly releasing pedal from 2,200 RPM to idle when in park or neutral.
Will attempt using professional OBD II scan tool to see if I can capture the event..
The AirFlow Meter is original...and it has been cleaned but it could still be marginal.
Oil Control Valves could be tired.
I could throw $1,000 in new parts alone, so am going to be judicious...
Noticed several postings concerning coggy upshifting and downshifting on 1998-2000 LS400's with A650-E transmission....
Aftee two decades and 160,000 miles of driving in a narrow RPM range, suggests the throttle position sensor as the culprit.(instead of Pedal Position sensor)
Transmission shifting was unLexus-like, ..especially on deceleration, yet no trouble codes..
The TPS is a mechanical device with a bearing and sliding contacts...with resulting wear over time ...and in a very narrow arc on the circuit board traces.
My TPS made an audible grinding noise so elected to replace... about $100 with tax for OEM Denso.
(If you use afterrmarket, then don't complain if it doesn't perform...just expect the worst.)
Noticeable improvement in shifting behavior with new Denso TPS...
Old OEM Denso Throttle Position Sensor with P.N. for ordering..
Well worth doing.
This probably would apply to any LS400 with125,000.+ miles....age-related oxidation is also a consideration.
Notice also the fuel gauge is not dropping as precipitously in stop and go City driving...
As a bi-directional.variable resistance mechanical device it is surprising no trouble code with lower threshold of degradation vs outright failure.
Reminder of ECT sensor resitive element degradation that does not ever seem to throw a trouble code...
I have a strange problem with my Lexus Ls400 1999. The gear shifts are not normal as it would shift at around 4000 rpm and second gear is fine but the third dont exist at all and it goes straight into 4th and thats it.
Also i cant see the PWR or ECT selection on the dash and even when selected i dont feel any difference in the drive.
Could it be the gear solenoids or maybe the whole gearbox. Can anyone suggest what to do here?
Can you take the old sensor apart,clean it with De-oxit and use a proper grease and just fix it? Would very much like to hear if its possible,Ive fixed other switches on vehicles with contacts issues.
Alternator pulley nvh damper to improve transmission shifting
Litens manufactures an overrunning alternator decoupler (OAD) or isolation decoupling pulley (IDP)
The IDP provides three functions. Its primary function is transferring torque from the engine to the alternator via the serpentine belt. It further provides an overrunning function during engine decelerations. And finally, it absorbs base engine torsional vibrations (firing pulses). The IDP not only provides a one-way clutch, it further incorporates a tuned torsion spring to absorb energy. The IDP rotates freely in one direction and have a “spring feel” in the other direction. The internal torsion spring is key to how the IDP performs It's third and most demanding job. The internal spring is tuned to absorb base engine vibrations (cylinder firing pulses) before they reach the alternator rotor and negatively affect the belt drive system. The IDP significantly reduces belt and tensioner motion, reduces NVH, and offers more durable belt drive system. OEM's such as Toyota/Lexus are incorporating IDPs in their accessory belt drives.
The pulley will rotate freely in one direc- tion and immediately lock in the other.
This type of clutch pulley allows the alternator rotor to coast any time the engine rpm decelerates quickly...such as transmission shifting
Installing an OAD on the alternator as a way to improve transmission shifting may surprise some, but merits further review...
01-21-18, 12:28 AM
1998 -2000 ls400 improved transmission shifting
