2000 LS400 Hard Shift 3RD when floored

[War165]

My ls400 has 198k, just recently replaced a solenoid because it was skipping 3rd gear entirely. Once in a great while when floored it’ll accelerate fine then when it shifts it slams into the next gear. I’ve tried it when floored on the highway and from a stop. 
 

it doesn’t slip gears at all, if I go slow it’ll shift into every gear smoothly but only when it’s floored. 
 

it doesn’t do it every time but only once in awhile. It’s a pretty hard shift, enough to feel like you’re being kicked..

when I did the transmission fluid change I used the correct fluid from the dealership. The magnets were also pretty clean for the mileage and so was the fluid. (Previous owner kept up on maintenance.

 

any help is greatly appreciated.

[Zeus253]

Try checking air vacuum connections, particularly the EGR plastic box (odd shaped) and the connection where intake air comes to meet the manifold throttle body. For example, in my 98 LS400 one of the many times I removed the big black piece connecting to throttle body manifold (near center of engine bay) ; I didn't make the rubber and hose clamp perfectly 100% and I had random things happen very briefly and intermittently. These events were: VSC off warning light, check engine warning, randomized low acceleration power, and most importantly - extreme automatic transmission gear change. Hope this helps!

[War165]

7 hours ago, Zeus253 said:

Try checking air vacuum connections, particularly the EGR plastic box (odd shaped) and the connection where intake air comes to meet the manifold throttle body. For example, in my 98 LS400 one of the many times I removed the big black piece connecting to throttle body manifold (near center of engine bay) ; I didn't make the rubber and hose clamp perfectly 100% and I had random things happen very briefly and intermittently. These events were: VSC off warning light, check engine warning, randomized low acceleration power, and most importantly - extreme automatic transmission gear change. Hope this helps!

Il have to check it out, my VSC light did come on a few times. I have an extra one in my trunk maybe replacing it would help with that one will help. 
 

also when I accelerate at times it does seems sluggish if I’m cruising around 40 50. 
 

il look into it thank you!

[mikaelse]

My LS400 was hard shifting when the fluid was probably 20 years old 95 kmiles.  It smoothed to normal after I did a complete oil change. The 2 Quarts out 2 Quarts in , drive for a day and repeat 6 times is recommended. 
Then most all old fluid is gone and it is back to red again.  I normally weigh what I got out and what I put in. The stick is finnicky and takes a while to be sure of level.  Easier to get right amount then. 

They say that you take a real risk changing the fluid after 100Kmiles on same fluid . You may have dirt deposits that may come loose with the new oils cleaning additives. 
If you have not changed the fluid for very long . Hmmm. Tough choise.