wont go over twenty miles per hour
Sounds as if you car is in limp mode, this happens allot when your car overheats , if thats the case you need to have the ECM reset...
Also have the catalytic converter checked, may be plugged.
This is the same problem I had. It is probablly in, "limp home mode." The car will automatically do this to protect the engine from damaging itself. In my case, the problem was a faulty knock sensor. Knock sensors are used by the engine to adjust the timing. If one is bad, it will not be able to adjust the timing correctly and it will automatically go into, "limp home mode." I have also seen this happen when the timing belt is bad and it is slipping. You should not drive the car at all! You should have a service engine light on. Get the codes read to pin point what exactly is going on. My code told me it was the knock sensor. After the sensor was replaced the problem was gone.
If it is your knock sensor, the stealership will charge you an arm and a leg to fix it. Check out this video where I show how to change them. It may save you hundreds. http://youtu.be/BhSTe75nP7E
Looking for a Used ES 300 in your area?
CarGurus has 948 nationwide ES 300 listings starting at $1,799.
Search Lexus ES 300 Questions
Lexus ES 300 Experts