Transmission Jolt When Decelerating

[99RXinRaleigh]

I recently purchased a 99 RX300 (2WD) with 90K. The car seems to be "jolting" when I slowly decelerate into a stop. It is definately a transmission shifting issue, because I can put the car into neutral and stop without any issues. If I come to an abrupt stop, it doesn't seem to happen. My check engine light is on, but the codes are leading to a Bank1 sensor 1 failure (I ordered the part from oxygensensors.com, just hasn't come in yet). Any suggestions on what could be going wrong? I just did the lexus tranny flush, but this didn't fix anything.

[dal]

I recently purchased a 99 RX300 (2WD) with 90K. The car seems to be "jolting" when I slowly decelerate into a stop. It is definately a transmission shifting issue, because I can put the car into neutral and stop without any issues. If I come to an abrupt stop, it doesn't seem to happen. My check engine light is on, but the codes are leading to a Bank1 sensor 1 failure (I ordered the part from oxygensensors.com, just hasn't come in yet). Any suggestions on what could be going wrong? I just did the lexus tranny flush, but this didn't fix anything.

One data point for you - I'm not an expert. On my 99 Rx300 2WD I had been experiencing some jolting - more on starting than stopping and when shifting from p to r, n to d, r to d, etc. starting around 90k Also had check engine light on and off for a while. Codes suggested Oxy sensor and Throttle Position Sensor. After having replaced, have not experienced the jolting. Other posts in this form discuss changing the Throttle Position Sensor - not overly complex - I did not do it. Not an expensive part. Just turned 109k.

FYI.

[wwest]

....Jolt...??

The transaxle will upshift as you slow to a stop and only after coming to a full and complete stop will it finally downshift into 1st gear. Some describe this initial upshift as a feeling as if being bumped lightly from behind.

It will also upshift at higher speeds when you fully release the throttle momentarily and that is described as the slingshot effect.

But I don't know as one could call it a "jolt".

These transaxles, seemingly, have a history of premature failures at 70-80,000 miles. While the owners manual has no recommendation for ATF maintenance many owners, myself included, are finding that the ATF is looking contaminated and smelling burned at ~40,000. Many dealers are responding to the problem by recommending flushing the transaxle every 15,000 miles.

There may very well be a "secret" warranty that covers these issues but insofar as I know neither Toyota nor Lexus has made any public announcements on these failures.

Reluctantly I would agree to flushing but at 30,000 miles.

My guess is that these failures are related to the fact that the transaxles upshift during even brief coastdown periods and now find themselves in the wrong gear ratio if the driver suddenly applies pressure to the gas pedal. Since the gas pedal is "hard-wired" on these early models the engine will instantly rise to acceleration torque levels as dictated by the gas pedal but in the meantime the transaxle is hurridly getting itslef into the proper lower gear ratio so as to not lug the engine down.

On a manual transmission how many times can you drop the clutch at high engine torque levels before replacing the clutch?

Same here.

So as of 2004 the RX uses a DBW system to prevent the engine torque level from rising until the downshifted clutches can have time to fully and firmly seat.

[99RXinRaleigh]

Thanks for the ideas, I'll check into the throttle position sensor if the condition doesn't change after I do the o2 sensor tomorrow.

[99RXinRaleigh]

Thanks for the ideas, I'll check into the throttle position sensor if the condition doesn't change after I do the o2 sensor tomorrow.

O2 sensor is done, check engine light is off, still shifting roughly only when slowly decelerating (other than that it is silky smooth)