RPM drops while in OD

Hello all!

family purchased my first tundra and loving it so far. However, something has come up which I’m looking into so that future problems won’t occur.

Issue/concern. I’ve noticed that while driving on the highway in OD, I will let my foot off the pedal completely, and the RPMs will from a few hundred on occasion. Not all the time, generally it will act like it just stays put at a slow deceleration as you would expect. Yet, sometimes even dipping 700 rpms but then it returns smoothly. I’ve done a lot of research on this and have seen everything from dirty MAF sensors, dirty throttle bodies, and even the “it’s a Toyota thing”. To the last options credit, I have had a 2005 Highlander for about 4 years and it currently has 240k. Bought with 179k and I’ve noticed that it does the same thing on occasion.

has anyone else experienced the same thing with their tundra? If so, what was the cause(s)? If you have one that does it as well, has it still made it to high mileage or is this a potential issue down the road that could prevent going 300k+?Planning to have a trusted tranny shop run their big boy scan tool to check the torque converter side out but it’s so random, it make me wonder about something being dirty or a random electrical trigger. Truck only has 95k miles, was babied, and serviced every 5k at a dealer so mechanically it’s been extremely well taken care of and not abused. As far as shift and driving goes, it’s very smooth.

Thanks for any input and help!

 

Are you saying you're driving along then let off the throttle and the RPMs drop? Thats normal. The torque converter unlocks when let off the gas. When you get back on the gas, rpms will come up and torque converter can lock again after a second or two.

 

^^^^^^^^^^^^
100% this

 

Yes that’s correct, but it’s at let’s say 70mph, sometimes letting off the pedal it stays locked and slowly decelerates, then other times it will randomly drop a few hundred RPM like it’s unlocking and cruising. The part for me is trying to figure out why it does it sometimes and doesn’t others, whether it’s the torque converter or something else causing it to do it randomly

 

If I’m in Tow/haul, it will stay locked and “engine brake” to help decelerate. The transmission may also have a grade logic sensor and programming to know when you going up and downhill.

 

That’s something I was curious about as well, because I figure it has to be something in the computer telling it when to lock and unlock and not a mechanical failure in the tranny itself

 

I also tested it in the “S” mode where you control the shifting and it was doing it while set in 6th as well

 

No mechanical issue. It's normal. I can watch it unlock and lock on my scangauge while driving.

 

Cool! As long as this is normal tranny behavior then I won’t worry about it anymore. And just to clarify, you observe it unlock at times and also stay locked at times as well under similar circumstances?

 

There are tables in the pcm that tell it when to unlock and lock based on transmission output rpm and throttle position, so the "sometimes it does it sometimes it doesn't" is just because you're at different combinations of rpm and throttle, and it also varies by gear and transmission mode. And it only take a few percent throttle angle or small rpm difference for the pcm to choose lock vs unlock, so what seems like similar circumstances will give different results.

 

Makes total sense. Thanks for the input guys!