Engine Hesitation.....more

[wwest]

I firmly believe that back in the early days of the RX300 (possibly earlier) they started using the torque converter lockup clutch for more than just OD.

Both my 2000 and 2001 AWD RX300 Lexus shop manuals seem to indicate that the lockup clutch is engaged anytime the vehicle is in cruise mode, no "high" level of torque needed from the engine or the torque converter/multiplier for acceleration. Disengaged only during acceleration, shift sequencing, and to prevent engine stalling during coastdown or slowing to a stop.

I have no question that using the lockup clutch in this manner, along with upshifting during coastdown or slowing to a stop, would have resulted in a significant level of additional fuel economy along with muchly improved emissions.

But.

Somewhere along the line they discovered that using the lockup clutch in this way, and/or upshifting the transaxles during coastdown, was to the detriment of the frictional surface of the clutch pack(s).

The first RX300 was shipped in 1998 and so the new fuel economy and emissions numbers are well entrenched in the public mind by the time these transaxles begin to show signs of premature failures. And how do you go about telling the public, the EPA and CARB that you screwed up and now you must recall a Gazillon Toyota's and Lexii to fix the transaxle firmware.

And oh, by the by, a simple firmware fix is available (only use lockup for OD) but would result in higher emissions and ~10% lowered fuel economy for this entire fleet.

So, by 2001 the engineers came up with a quick and dirty solution. No time to road test.

DBW, e-throttle.

"If we can prevent the engine from developing high levels of torque while these clutches are engaging and disengaging then their frictional surfaces will not wear out prematurely...."

What is that movie that's out on DVD now....??

Something about unintended consequences.....

So, if I am correct then a FIX would of necessity apply to the entire Toyota and Lexus FWD fleet from at least 1998 forward.

Good luck seeing a fix this century.

[RX in NC]

So many theories, so few solutions. I wish we knew the actual details but we never will. It would cost Lexus a fortune.

I've tempered my fury at Lexus Corporate somewhat over the past six months and I've adopted the attitude that I can't re-engineer or modify the transmission, but I can certainly change the T-IV fluid every 30,000 miles and I know that my wife will continue to drive cautiously and carefully as is her nature.

If we can milk 130,000 miles or so out of this albatross and then unload it, I'll consider it as mission accomplished and lesson learned. Especially with our local Lexus service manager having approved and covered every single malfunction that's arisen to date (they have been numerous as well as major). I know that we are quite fortunate in that regard compared to everyone else out there with the same symptoms and problems who aren't getting the same goodwill coverage we've received. Other than routine maintenance, the only money I've spent on this thing has been for new tires and new brakes.

[wwest]

Changing the transmission fluid will not extend the life of the clutch frictional surfaces. Putting in new fluid will allow the hydraulically actuated valves, pistons, etx, to return to normal operation.

The fluid you remove is contaminated with the residue of the clutch frictional surfaces which has prevented it from functioning properly, purely as a hydraulic fluid, as was intended.

Whichever frictional surface, or surfaces, is wearing at an undue rate will continue the same wear rate and the transaxle will therefore still fail prematurely. Certainly not as soon as it would if the fluid were allowed to continue to degrade but fail it will.