Last post on Oct 19, 2009 at 10:32 AM
You are in the Toyota Sienna
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Toyota Sienna, Transmission, Van
#1 of 38 Slipping/Non-responsive Throttle in 2007 Sienna
Oct 30, 2007 (1:20 pm)
I rented a Sienna this summer for a drive to Canada. It was very responsive to throttle changes. I love it so much I ended buying one. Unfortunately, my purchased vehicle has poor throttle response. The engine revs, but the van does not pick up speed right away. I experience a huge delay in response. Anyone else experience the same problems? Seems like the torque converter is not coupling properly.
#2 of 38 Re: Slipping/Non-responsive Throttle in 2007 Sienna [drhsu]
Oct 31, 2007 (10:41 am)
I would take it back to the dealer, to see if a TSB covers this issue.
Our 2007 is fine, no hesitation. Plus you feel a difference so this is not normal operation.
#3 of 38 Re: Slipping/Non-responsive Throttle in 2007 Sienna [ateixeira]
Nov 01, 2007 (12:28 pm)
Thanks for the suggestion. I will take it back again and maybe ask them to compare it to another one.
#4 of 38 Re: Slipping/Non-responsive Throttle in 2007 Sienna [drhsu]
Nov 10, 2007 (6:30 pm)
I seem to have a very similar problem on my New 2008 Sienna. I waited until I had 1200 miles on it before bringing back to the dealer. Of course, the dealer said there was nothing wrong--ooh what a surprise! The problem I experience is the throttle not responding especially at around 6-8mph. I literally step on the gas for 2" or more and no response (like it is in neutral), then it will lurch up to the next gear. I will also get this reaction when I'm driving along and then coasting, and then I step on the gas with very little response until I press down at least 2 or more inches.
2 experiences I had at the dealer... 1) they told me that since the gas pedal is not electronically controlled and nt by a cable, it has a slower response time (logically this makes no sense to me!) 2) I test drove another 2008 XLE sienna, and it had the exact same response as mine.
I am extremely disappointed that a high-end van like this could have such POOR performance. Every time I get into my car, this is all I think about! I owned a 2001 sienna, which was peppy and responsive.
I'd love to hear from others and their expereinces..........
#6 of 38 Re: Slipping/Non-responsive Throttle in 2007 Sienna [prinesurf]
Nov 14, 2007 (11:33 am)
When you say no response, do you mean the engine rpm did not change, or the engine responds but the vehicle does not react immediately to the change in engine speed (do not feel any acceleration)?
My experience is the engine picks up speed right away, but do not feel any acceleration for a second or so. This is especially so when:
1. I go over speed bumps at a slow speed, and press on the throttle after going over the bump,
2. When I lift off the throttle approaching a corner, and pressing on the throttle half way through the corner. Feels like the gear slipped into neutral (engine roars, but no acceleration.
#7 of 38 Re: Slipping/Non-responsive Throttle in 2007 Sienna [ateixeira]
Nov 14, 2007 (11:42 am)
Thanks for the info. I will give it a try. Given that in my case the engine rpm did respond immediately, I am not sure how much difference I would experience with this mod.
I do not have much clue as to what the computer controls these days. Does anyone know if the computer also controls the torque converter in the 07 Sienna? To me, it feels more like the engine side of the torque converter spins but the torque takes a while to transfer to the drive shaft side of the converter. Wrong spacing? Wrong transmission fluid? Off-spec transmission fluid?
#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".....