keerc

My 1993 lexus 400 has been performing great, until lately... it started with a jerking action at road speeds between 30 and 65 mph. It runs great at other speeds... when the jerking action begins, an adjustment of the gas petal stops the jerking, changing the load on the engine..

. i cannot tell if the problem is ignition or fuel ... It has full power and idles great. But, the jerking motion is very noticeable and is probably strong enough to cause breakage of the power train...

I drove the car about a hundred miles today, and it was worse than the sixty mile trip of yesterday...

Can anyone help with suggestions ??

The car has always beens serviced well and has been a good car...

I searched the forums, and could not find this problem listed... If you can find a former posting for me, I would very much appreciate it...

RA40

iTrader: (6)

If the engine is running smoothly, the likely cause is further down in the driveline. How many miles on car? When was the last tranny fluid service? Any strange noises when this occurs?

Lexinky

X2, it may be the the torque converter or some other transmission related issue.

Torque converters will sometimes shudder at mid range speeds under light acceleration as they lock and unlock.

keerc

I cannot tell if the engine is the culprit... the jerking action is about two jumps per second and only happens after the engine is at normal op temp and the car is in overdrive with very light load. The jerking stops if I accelerate or de-accelerate... If I remain at the same speed, the jerking continues... Any change of the acceleration of the car stops the jerking for a couple of minutes.

At times I can drive for fifty miles and there is no problem, and other times the jerking starts with ten miles from a cold startup.

I think that the jerking action is too severe to be the torque converter unlocking... it is more like the engine in totally shutting down for a fraction of a second each time it jerks.

I cannot find a problem with the ignition and the fuel supply seems to be plentiful, as the car accelerates very well with no pausing or skipping. It idles very smoothly and starts like new...

Could the EGR be at fault ??

I know the computer could do this, but I do not have a replacement, and dont want to buy one and still have the same problem...

thanks guys for your help..

bob

keerc

BTW: Mike, my car looks exactly like your avatar except the wheels....

the car has approx 177K miles, but had an engine rebuild about 55K ago... and has been serviced very well... this is the first problem since the engine rebuild...

keerc

thanks for your reply... the car does not jump as much if I manually lock out overdrive, but still jumps at normal driving speeds with light load... shifting the PWR tranny switch also does not change the jumping...

Is there a way to lock/unlock the torque converter manually ???

I am afraid that the jerking motion is going to break the drivetrain if I continue driving it, but it is not worth spending a Lexus shop repair...

RA40

iTrader: (6)

What RMP range and any gear this occurs with repeatable frequency? How is the tranny fluid? Past threads have had some positive changes when the fluid is drained and fresh is cycled through. These are low $ attempts so if the fresh fluid doesn't bring changes you can work your way up.

Though extreme, this may be a thread to have in mind if ECU related.
https://www.clublexus.com/forums/ls4...es-solved.html

keerc

normal rpm at any speed from 30 to 55 mph... as long as the car is moving at a constant speed... the jumping stops completely at 65 mph and runs great at any speed above 65 mph and under 30 mph... the problem still occurs with OD turned off and at the same road speed... looks like not not directly related to engine rpm except within the range listed...

transmission fluid/filter change approx. 20K miles ago. Fluid still looks new and at proper level.

Transmission shifts properly and smoothly. OD shifts properly and unlocks smoothly...

Seems that problem is more related to engine rpm at constant value.

BTW: the computer was serviced by a guy on EBAY 18 months ago for another reason... possiblity he did not complete the job... I will pull it and inspect the caps... should have done it myself the first time since I am a retired electronics engineer, but at the time, did not 'feel' like it.... my bad...

thanks again...