Hesitation

[wwest]

Solenoids alone aren't necessarily the primary delaying factor.

It's more likely the valve body hydraulic sequencing along with the actual time it takes to release the clutches from the previous gear ratio, give them time to actually fully release, hydraulic pressure to bleed off, and then "order" the proper set of clutches for the new gear ratio to be engaged, pressurized, and the wait for them to be fully engaged.

Think of the time it takes with a stick shift, assuming you want your manual clutch to have a long life.

Get off the gas, and disengage the clutch (unlock the torque converter) take the shifter out of the previous gear (release the hydraulic pressure on the clutches for the previous gear and wait for the "return" springs to force them open.), slide the stick into the new gear (pressurize the clutches for the new gear ratio, and wait for them to engage), release the clutch pedal and apply appropriate pressure to the gas pedal (heavy gas pedal pressure, or closed throttle, leave the torque converter unlocked. Gas pedal positioned for cruising, lockup the torque converter).

"-Why did/does the 4-speed auto not have this issue..."

I have argued that it actually does.

But in a different "form".

I have no doubts whatsoever that the transaxle in my RX upshifts if the throttle is fully closed during highway coastdown and just before coming to a full stop. When it does and I re-apply pressure to the gas pedal it must now downshift.

The transaxles in the previous model, the RX300, seem to be failing prematurely at an unusually high rate. I have reported that the transaxle fluid in my RX was burnt and dirty looking at 38k miles and apparently Lexus has revised the recommended maintenance schedule from NONE to every 15,000 miles to address some here-to-fore unknown flawed operational aspect of these transaxles.

My RX has a mechanical throttle connection so the throttle valve cannot be closed during a transaxle shift sequence. Can Lexus temporarily "detorque" the engine some during the shift sequence?

Stop the ignition ? = RAW gas & air mixture into the exhaust stack and catalytic converter.

Disable the fuel injector power? = PURE oxygen to the exhaust stack and catalytic converter.

Considering the EPA's and CARB constantly changing, updated, emission standards are either of the above choices viable. What are their long term effects on the oxygen sensor and/or the catalytic converter.

Suppose the firmware in my RX series, with an engine that cannot be dethrottled for 1 to 2 seconds, doesn't have an embedded wait delay to be sure the previous gear ratio clutches are fully released before engaging the next "set". That would result in BURNT clutch frictional surfaces, burnt and "dirty" looking fluid, and eventual failure of those clutches.

What's the most economical fix to prevent premature transaxle failures in the newer models?

DBW.