okay so my 95 ucf20 always had a transmission that a few hiccups due to the rotten ECU, which i ignored and just drove the car 5 years without replacing. eventually it lost 4th gear totally and i changed the ECU. ta-da! 4th gear came back and the car never drove so insanley well! unfortunatly it was very short lived, and i mean VERY short. 1 day later it was slipping between 3-4 again as well as grinding. day after that the tranny let go completely and its been sitting in my driveway ever since.

the problem i had was totally preventable -according to multiple opinions both proffesional and unprofessional, that the tranny failed simply because of the ecu freaking it out running it wrong for so many years. which now brings me here..

Imperial Jade 2000...

this car is the same age as the 95 was when i bought it. first gear is fine, however second gear feels sluggish and i absolutley have to nail it for it to really move. when floored it accelerates jerky and sometimes slips between 3-4. this is intermittent. its different every time i drive the car. sometimes its totally normal but sometimes it does this hiccup crap my 95 did. i thought the ECUs in the 98-00s were better then the 95-97s and didnt go bad? why is this happening?? the car has 167k on the clock and was absolutley babied by an 85 year old man its whole life, who replaced EVERYTHING when it broke, so this one didnt have a hard life. theres no way the tranny could be bad in this car too, am i crazy?? and the jerky acceleration.. why? this last gen model was drive-by-wire wasnt it? could a sensor be causing this to happen? this is my 10th LS400 as well as the first one i havent absolutley hooned to death and neglected the **** out of the entire time i had it, as my newest/most well cared for example. im actually taking care of this one as i had planned for it to be my last DD Ls400 so i want it to last as long as possible. ive only had it a few months and replaced Tbelt/Wpump, as well as drive belt and front main seal. i also had the trans mount replaced. i paid $3800 for the car plus an extra $1500 in new parts and other work. it really gunna burn my *** if the tranny takes a giant dump on me at 167k. any advice? is this a sensor/ecu issue or did i just pick a stinker?

 

So how do you know its the transmission and not the engine? Aren't you the guy that works at a lexus dealer? I'd hook up to a good scan tool and watch how the shift solenoids are being powered when all this slipping happens. Hiccup is more engine drivability related ?? Again scan tool and drive and have someone watch whats going on.
It could be lots of different things going on, and to rule out ecu activity and solenoids you need the scan tool first. If you take it to like a transmission shop they will drive it and say yup you need a rebuild. And then if its simple solenoid or what ever, they will tweak it and charge for the rebuild, I used to know a few that would do that.
That is similar to the oil change places that don't change the oil and charge for it.

 

Have you done any drain and fills of the trans fluid? Also, replace the pan filter. You probably should check the engine mounts also.

 

One thing I can say is that a 98-00 ECU tends to show unusual AT shift problem when it is failed. But the failure rate is much lower than earlier models. See my post #1454 at the capacitor thread which you can find it at top of the sticky now.