Need Help! Engine Problems w/ my 1st gen LS400...

A little background on this... It's a '91 LS400 w/ 59,000 miles on it, which I bought from an old Japanese guy a few months ago. He only used the car to go to doctor's appointments and grocery shopping. Car is in immaculate condition inside and out. Engine bay is clean as a whistle. And it was serviced by Lexus 2 months before I purchased it.

First thing I noticed after purchasing it, was that the TRAC light went on after I drove it from the guys house. Then on the freeway, it felt a little jerky trying to maintain a speed around 45mph-55mph (between 1,000-2,000rpm). But any speed below 45mph, or above 60 mph would be a smooth ride.

After several months of that, the problem seems to have gotten worse... Now, every time I start up the car, the rpms seem to fluctuate a bit, and the engine seems to be shaky whenever I roll out of a parking stall... Not too long after I start to drive it... whenever I'm idle, the rpms fluctuate again. It's not until I've driven for a few minutes that the rpm fluctuation stops.

Even on the freeway, it's gotten worse... a lot of times, my engine seems to be struggling a bit to pick up speed (especially if I'm following a car going on an on-ramp, or for some odd reason, when I try to pick up speed after making a left turn). And when I try to maintain a speed between 45-60mph, the ride is still jerky... sometimes the whole car seems to lunge back and forth and shake.

I've had my car checked out by all my mechanic friends, but they really don't know what's up with it. They suggested I might just need a tune up... But I dunno. If any of you guys have any suggestions, or know what's up, let me know. Thanks in advance. Peace.

Do a drain and fill on your transmission fluid asap. Pan only. 2.3 quarts. Your fluid is old, and the jerking when trying to accelerate is what clued me into it. Same thing happened on my old ls400. 

After you do the first drain and fill, it should ride smoother. Then, every time you change the oil, do a drain and fill at the same time. Keep doing it until that fluid is the nice cherry color going into the transmission. Then you can switch it to every few oil changes do a drain and fill.

[QUOTE=Caoboy;169023]Do a drain and fill on your transmission fluid asap. Pan only. 2.3 quarts. Your fluid is old, and the jerking when trying to accelerate is what clued me into it. Same thing happened on my old ls400. 

After you do the first drain and fill, it should ride smoother. Then, every time you change the oil, do a drain and fill at the same time. Keep doing it until that fluid is the nice cherry color going into the transmission. Then you can switch it to every few oil changes do a drain and fill.[/QUOTE]

+2, I had a similar situation with my second gen. LS. After flushing the transmission fluid and tossing in a new battery it was good as gold. :thumbsup:

I also got the transmission on my ls flushed and they changed the tranny filter as well.  It made a world of difference.

Thanks for the info guys. Much appreciated. I'll be doing this first thing tomorrow, and let you all know how it goes. Thanks again.

Check the wires on the left side of the trunk hinge and check all the ground wire in the trunk.  Its a common LS problem.

Check the Idle Control valve common problem for Toyotas that will cause your car to miss idle when you first start it. Easy fix to just remove it and clean all the gunk out of it with parts cleaner.