1999 ES 300 Lexus check engine light on and Over drive Off

Last month I changed all spark plugs and two ignition coils and after few days both The lights for Trac Off & Check engine light, are on. if I clear it by disconnecting battery its back after few miles driving and When I drive on the highway RPM is more than 4000. The code is for knock sensor, and according to mechanic the high RPM is not due to knock sensor, its some other electric problem. Two transmission specialist also checked it and both said transmission is working fine.

Just went thru the same thing, with the same Lexus. Changed the temp control sensor, Easy to do. Computer is getting a false reading as to what the temp of the engine is causing not to shift until completely warmed up. Knock sensor are an expensive fix if it's that problem...

The speedometer is working, don't have the code but will get it scan and get the code, but I remember he said the code is for knock sensor which he cleared, but after few miles the Trac Off & Check engine lights are back. As suggested will try to change the temp control sensor, hope it will also work for me.

Thanks for the answer, just one question before I change Temp sensor, in your case what was the reading of temp gauge, in my case the temperature gauge is always below the half mark, you still think I should put a new one.