Last post on Oct 19, 2009 at 10:32 AM
You are in the Toyota Sienna
What is this discussion about?
Toyota Sienna, Transmission, Van
#8 of 38 Re: Slipping/Non-responsive Throttle in 2007 Sienna [drhsu]
Nov 15, 2007 (8:20 am)
I'm going to guess that it's just choosing the gearing.
They're set up for peak efficiency, not peak performance. When you let off the throttle before a speed bump, it might shift from, say, 2nd to 3rd, all to save on fuel.
Then you hit the gas and the gear is too tall to accelerate like it would have prior to the speed bump.
The "hesitation" is basically the time it takes for the transmission to shift back to 2nd gear.
If you floor the throttle to compensate, what probably happens is it shifts not once, but twice, and ends up in FIRST gear. So basically the double-shift takes longer, and when it does get in to first gear you notice a sudden surge of acceleration.
Top it off, I bet the ECU dials back the throttle a little to help preserve the transmission, for powertrain longevity. So it shifts, shifts again, then dials back the throttle-by-wire so it doesn't slam in to first gear.
That excaberbates the feeling of hesistaion. You have nothing, nothing...then WOW you get a lot of acceleration.
I would try rolling in to the throttle gradually, so it knows you only want 2nd gear, not 1st. I bet it takes less time to perform that one shift and 1/2 throttle vs. the two shifts at full throttle.
This is pure speculation on my part, of course.
#9 of 38 Re: Slipping/Non-responsive Throttle in 2007 Sienna [ateixeira]
Nov 15, 2007 (9:02 am)
Most interesting theory. What I should try is to set the gear manually to '2' and see if any of the mis-behavior still occur. If your speculation is correct, I should bypass all the hesitation and gear shifting issues, correct?
#10 of 38 Re: Slipping/Non-responsive Throttle in 2007 Sienna [prinesurf]
Nov 15, 2007 (10:17 am)
You folks are discussing, seemingly, the latest iteration (Wow, 2008..??) of the infamous Toyota/Lexus 1-2 second transaxle downshift delay/hesitation.
Late in the last century, to conserve fuel, and possibly more importantly, to reduce the heat loading of the ATF, Toyota adopted a sub-standard sized positive displacement gear type ATF pump.
The lower capacity pump could not supply enough volume/pressure to support "HARSH" gear changes, mostly downshifts in this case, so the engineers sat out to eliminate those.
Unsuccessfully so, as it turned out, drivers will do what drivers have always done, ask for GO power at the most inconvient times. So early models, '99 RX300, with/of this "experiment" had a few premature transaxle failures.
So Toyota adopted DBW to "protect the drive train". DBW is being used to delay the onset of engine torque in response to foot pressure on the gas pedal until the downshift, starved for adequate ATF pressure, can be fully completed with the engine at or nearly idling.
Ford, on the new Edge, has adopted a variable displacement ATF pump as a solution to this very same problem. Maybe Toyota will "listen"...??
Ten years and Toyota is still "experimenting".....
#11 of 38 throttle response
Nov 15, 2007 (10:27 am)
If I may make an observation. I have an 06 Mustang GT that is heavily modded and one of the biggest improvements was re flashing the ECU or computer to improve throttle response and with those who have auto's gain a lot of torque off the line. Not to mention advancing the timing and many other things. Now of course this is a bit much to do to a van but the same principle applies that the computer controls the throttle body and also the torque converter. It seems that most if not all new cars have these "smart" computers that learn your driving habits and adapt the vehicle to you needs. It seems that this "learning" killed throttle response on a lot of people who had stock Mustangs. The answer without modding was to disconnect the negative off of the battery and let the car sit for 20 min or so, enough time for the computer to forget all that "learned" info. Reconnect the negative and off you go. You would also know the computer has been reset by the idle being a lot higher for the first 5 or 10 min of operation and then it settles down. I think it would be a smart place to start, just don't forget you have to kill power to the ecu long enough for it to reset its memory.
#12 of 38 Re: throttle response [lavrishevo]
Nov 15, 2007 (11:52 am)
Good responses, both of you.
The drive-by-wire only support my theory, because it only means Toyota has even more control of what the engine will do (and the driver has less).
I've advanced the timing on my Miata the way lavrishevo descrives, but those days may be behind us as newer cars retard/advance timing on their own, using input from knock sensors for instance.
I'm not sure if you can manually set the timing on the 2GR V6, but I doubt it.
#13 of 38 Re: throttle response [ateixeira]
Nov 15, 2007 (12:22 pm)
I tried setting the gear to '2' going over the bumps and going around the corners and the hesitation is mostly gone. This seems to bear out the theory that the transmission is trying to figure out what gear to use. Interesting that the rental one I had did not exhibit this behavior.
Anyone has any program to flash the ECU of the Sienna to get improved throttle response? If the transmission can take it, the Sienna will be a great sleeper car - with 266 h.p. and a five speed transmission, it can out accelerate a lot of cars. Any tuners out there willing to try it?
#14 of 38 Re: throttle response [drhsu]
Nov 15, 2007 (12:28 pm)
I'm not sure, but I think if you're in 2 it will allow 1st or 2nd gear.
Did you observe that? Or does it force a 2nd gear start, even from a dead stop?
#15 of 38 Re: throttle response [ateixeira]
Nov 15, 2007 (1:10 pm)
I am sure it can go down to first gear. Since I did not come to a complete stop for the speed bumps or for the corner, I think it stuck to 2nd gear. The engine rpm stays above 1500 rpm the whole time and does not change much when I press on the throttle after the bump or while in the corner.
When set to 'D', when I approach the corner or the speed bumps, the rpm drops down to close to idle. Pressing on the throttle result in the rpm going up to 2000 or so without instant change in acceleration.
#16 of 38 Re: throttle response [drhsu]
Nov 15, 2007 (1:41 pm)
So manually selecting the gear does help.
We should do that or at least roll in to the throttle gradually.
#17 of 38 Re: throttle response [ateixeira]
Nov 15, 2007 (2:25 pm)
Going into a corner without lifting off the throttle completely helps to minimize any lag. What is interesting is the rental did not exhibit this lag. I hope someone can come up with a modified program to flash the ECU....