I have a 1999 ES300 with 140k miles. Car drives. It takes about 5 minutes for the car to shift into overdrive. After some time driving, the car will not engage overdrive at all, making it very bad to drive at highway speeds. When this happens the car will often not downshift even if I put my foot to the floor.
Even worse, sometimes the car will get stuck in overdrive, so it is very difficult to start from a stop. (If I shift into R and back to D it remedies the problem)
What's wrong? Solenoid? Fluid?

 

Can you drive your car around on the street for about 20 minutes? If so, then drive it around and check the level of the trans fluid while your car is idling. Check to see if the level is good and take note of the color of the trans fluid. Make sure when you check the fluid you are on a level ground.

 

Drain the fluid and replace with Toyota type T-IV fluid if you got the money or castrol import multi-vehicle atf if you're tight on cash. Don't flush it just drain and add back what ever you drain and check the fluid following crisp76 instructions. The transmission also has a kick-down linkage for downshifting that is attached and adjusted from the throttle linkage.