"lurching" At High Speeds When Reaccelerating

[rtd111]

91 LS400, 240K miles

When driving at freeway speeds, for example, past 50mph, when I release the gas pedal and then hit it again (however softly or aggressively), the car seems to skip a beat on the transmission. It looks like its downshifted an extra gear, and then reengages up two. Gives a subtle lurch.

With OD off, when cruising without pressing on the gas pedal, it doesn't seem like its runnning in 2 though -- rpms still stay around 2K (like they don't jump to 3K, like they do when running at these high speeds with OD off).

It drives fine when in overdrive is off: no lurching, and rpms over 3K all along.

Car seems to drive without any issues in city driving.

Any ideas?

[steve2006]

You don't say which year your car is but firstly pull the transmission diagnostic codes and see if that tells you anything, check the transmission fluid for correct levels and is it due for replacement?

[nc211]

Wierd and goofy stuff like this in your model year series, sometimes are directly related to the "black wire" in the trunk. There is a black wire that runs along one of the hinges of the trunk. Over time, it can either break, or the insulation gets shaved off, causing a funky short in the system. Search for "trunk wire" on here to find several other threads about it, how to find it, how to fix it "it's easy".

Other possiblity is the transmission fluid itself. Might be due for a fresh dose of genuine Toyota type iv fluid.

[rtd111]

Wierd and goofy stuff like this in your model year series, sometimes are directly related to the "black wire" in the trunk. There is a black wire that runs along one of the hinges of the trunk. Over time, it can either break, or the insulation gets shaved off, causing a funky short in the system. Search for "trunk wire" on here to find several other threads about it, how to find it, how to fix it "it's easy".

Other possiblity is the transmission fluid itself. Might be due for a fresh dose of genuine Toyota type iv fluid.

Thanx for both replies.

I did put the year: its 91.

I should have mentioned: a transmission services was recently performed to see if it would fix the problem: just the fluid was flushed and changed. Nothing more significant than that.

Separately, if it matters, the steering rack was replaced. Not sure what the reason was. BTW, I do not own this car: it belongs to a friend.