I've been a Lexus Owner's Club Member since 2005, not sure how I've missed this great forum all these years. my 1998 LS400 was taken away from me too soon with 337k miles a couple of weeks ago. I believe that these cars can almost "last forever" when cared for.

I replaced the car in a hurry with another '98 with 189k miles. This car had been neglected for the past 100k miles. Amazingly, the starts and runs fairly well. I am sorting out the issues one at a time.

The car is shifting with a jerk, usually when the engine is warm, at various speeds, but most noticeably around 50 mph. It happens even when I am trying to hold speed, I must be right at the shifting point.

I do intend to drain and refill a couple quarts of tranny fluid at a time, though the current fluid is nice and deep red with no burnt smell. I also know that the former owner recently had Lexus replace a VVT solenoid. I am in the dark on the purpose of the solenoid but something tells me it was to address the shifting problem.

On my 1991 I remember dropping the pan, cleaning it and replacing the gasket to re-install.

Is the procedure the same for my 1998? Is there anything else I should be doing? I'd hate to know that my transmission is gone...

 

VVT solenoid is unrelated to the shifting issue. I recco the following things to address your shifting issue, that also fall under general maint.

1-clean the throttle body along with the idle ports, there's a thread on this in the faq
2-replace the rear engine mount (aka the transmission mount), total cost is low and very doable in your driveway with a jack/stands and basic tools.
3-drop the pan, clean the filter, and reseal pan with toyota FIPG (orange, not black). Same procedures as what LexLS has in the bible.
4- as you mentioned, only use toyota T-IV fluid.

 

PureDrifter, I remember you from awhile back, good to see you are still here. Funny, I had already ordered and paid for the tranny mount. I also plan to change the engine mounts, the vibrations are obvious. The throttle body was dirty. I didn't realize it could cause such a significant and noticeable shifting problem, but will definitely clean it up. I hope the procedure is similar enough for this and dropping the tranny pan, as it is on the earlier cars? I remember following the easy tutorials on lexls.
Is it safe to clean the MAF sensor? I don't have any CEL's now, but do have a drop in mpg that I didn't have on my last '98 with double the miles. The throttle body cleaning I realize may help. I also plan to change the spark plugs, fuel filter, air filters already done, not sure what else...some say 02 sensors may not be optimal but I'm not going to spend the $ there.

 

leave the MAF for last, cleaning it can be done if you use a cleaner made for it and follow the directions, but it is still somewhat risky.

Throttle body cleaning is different from the LexLS link since ''98-00 cars have them in the front of the intake. The idle ports are under a small metal plate held on by two phillips screws.