My Lexus ES300 has been having this intermittent problem for approximately two years....it will not shift into 4th gear..at first my mechanic and I thought it was an ambient temperature problem because it seemed to happen in the cold weather...as of this date (7/201/2018) the problem is still occurring..it has also started "bucking"..it can run perfectly for a day...my mechanic has been dealing with this problem since the above mentioned time period and has addressed all the codes...our latest "repair" was to "splice into one knock sensor" therefore only using one knock sensor.(their are two) .this only worked for awhile...my mechanic is quite versed with Lexus products & people from Lexus even call him for advice...he believes their is a "glitch" in the computer program...the car has had a new transmission as well as a new computer in the past; to no avail..it's a shame because this automobile looks like it came out of the showroom yesterday (obsessive compulsive)!! Any suggestions???

My only issue, outside of what my complaint is, is that with Lexus models (that I know of), once the check engine light appears, Traction is automatically off and stays off.

As far as the problem, my mechanic thought it was the Knock Sensor. We replaced the knock sensors (which were new), the connector and the intake gasket. Drove the car around and the issue is still persisting (not to mention the P code still appearing for the knock sensor).

What happens is after driving for more then 15 minutes, every time the car shifts a gear up or down, the car stalls, as if my feet aren't on the pedal and the car slows down. After about a few seconds (between 2-30), it jerks back into gear (everyone within the car can feel it). Sometimes as this issue is happening, in idle, the car shakes heavily, which obviously isn't normal for a Lexus. I've gotten other codes, that I plan to get fixed within the next few weeks, but for the most part, myself, my mechanic and his boss think it may be the Transmission and not the other issues that are causing this.

Trying to figure out if replacing the transmission will fix the issue because I prefer to keep this car for another 7-10 years (or trade in to get an LS400 pre-1999).