1991 LS 400 transmission jerking?

[:\) :\)]

Hello:) Just bought my first lexus today and am unsure on a few things.
When I am between the 40 and 45 mph range and trying to drive that speed
the car jerks. Its fine if I go right through that speed all the way to
50 or higher. Could this be a transmission issue or maybe the throttle
body that needs cleaning? It seems like the car is confused whether or
not to upshift. Thanks in advance for the help!! :)Nat

[Ray O]

Post by :\) :\)
Hello:) Just bought my first lexus today and am unsure on a few things.
When I am between the 40 and 45 mph range and trying to drive that speed
the car jerks. Its fine if I go right through that speed all the way to
50 or higher. Could this be a transmission issue or maybe the throttle
body that needs cleaning? It seems like the car is confused whether or
not to upshift. Thanks in advance for the help!! :)Nat

The jerking could be caused by the engine or it could be the transmission.

What is the condition of the automatic transmission fluid? If it is not
bright red, you may wish to change the transmission fluid. If a service
facility tries to sell you a transmission flush, you should politely decline
and go for a fluid change only. The jerking could the torque converter
locking or unlocking or it could be a bad accumulator.

It could also be related to the EGR valve. To check this, temporarily
disconnect the vacuum hose from the EGR valve and plug the hose with a golf
tee or screw and see if the jerking goes away. If it does, then the EGR
valve may be acting up or the EGR control circuit could have a problem.

The throttle body will not cause jerking.

[:\) :\)]

Hello RayO:) Thank You so much for the reply!! I will check the fluid
today and try to find the egr and attempt what you have told me. I will
post my findings. Thanks again!! :)Nel

[Ray O]

Post by :\) :\)
Hello RayO:) Thank You so much for the reply!! I will check the fluid
today and try to find the egr and attempt what you have told me. I will
post my findings. Thanks again!! :)Nel

you're welcome!

[mcbrue]

I have noticed this same thing, sort of, in two ES3xx models and in my
current 06 LS430. It seems there is a shift point somewhere around 45
and the car sort of hesitates or something around there if it is just
lazing along. When I have my foot on the gas and am driving steadily or
even accelerating I don't notice it. But if I take my foot off and let
it sort of coast before resuming gas feed, then I notice it. Hard to
describe and may not be the same thing you are experiencing. But my
Lexus store says that is normal. Of course my rough brakes and tranny
are normal to them, so maybe Ray O knows a bit more than my guys.

[Ray O]

Post by mcbrue
I have noticed this same thing, sort of, in two ES3xx models and in my
current 06 LS430. It seems there is a shift point somewhere around 45
and the car sort of hesitates or something around there if it is just
lazing along. When I have my foot on the gas and am driving steadily or
even accelerating I don't notice it. But if I take my foot off and let
it sort of coast before resuming gas feed, then I notice it. Hard to
describe and may not be the same thing you are experiencing. But my
Lexus store says that is normal. Of course my rough brakes and tranny
are normal to them, so maybe Ray O knows a bit more than my guys.

If you lift your foot from the throttle and then press on the throttle pedal
again, the torque converter will unlock to allow torque multiplication
during acceleration.

[:\) :\)]

Hello RayO:) Ive checked the fluid and it looks and smells like it was
literally just changed a month ago. Should it be dextron(the red fluid)
atf? I looked at the egr valve diagram under the hood and tried to
match it up to the items on the engine. There is a round thing with 3
vacuums going into it and each port has a letter. One of these vacuum
lines goes back to what I believe is the egr valve with an electric
connector and 2 vacuum lines hooked up to it. There is a 3rd vaccum line
connection that faces the firewall but it had a plug on it already that
looks to be a factory plug? Should I unplug both of the other vacuum
lines and cap them off? I did open up the aircleaner housing to check
the airfilter and have never seen such a dirty airfilter as this..there
was even large winged flies stuck on it. I will clean the tb tomorrow
and get a new air filter as well see if this helps any. .... Thanks
again:)

[Ray O]

Post by :\) :\)
Hello RayO:) Ive checked the fluid and it looks and smells like it was
literally just changed a month ago. Should it be dextron(the red fluid)
atf? I looked at the egr valve diagram under the hood and tried to
match it up to the items on the engine. There is a round thing with 3
vacuums going into it and each port has a letter. One of these vacuum
lines goes back to what I believe is the egr valve with an electric
connector and 2 vacuum lines hooked up to it. There is a 3rd vaccum line
connection that faces the firewall but it had a plug on it already that
looks to be a factory plug? Should I unplug both of the other vacuum
lines and cap them off? I did open up the aircleaner housing to check
the airfilter and have never seen such a dirty airfilter as this..there
was even large winged flies stuck on it. I will clean the tb tomorrow
and get a new air filter as well see if this helps any. .... Thanks
again:)

I believe that the automatic transmission fluid (ATF) is Dexron III.
Hopefully, the previous owner just changed it and did not flush it.

The EGR valve will have metal tubing leading to one of the exhaust manifolds
and to the intake manifold. Unplug and block all of the vacuum lines
leading to the EGR valve.

The symptom of a dirty throttle body is usually a throttle that sticks
closed, without any noticeable drivability problems.

[:\) :\)]

Hello:) Thanks for the input. Mine is slightly a different problem. I
have to stay steady at that 45mph mark and it will buck. If Im going 40
and am slowly going by the 45mph mark it will not do it nor will it do
it at 42mph or 47mph..strange:) Thanks again:)