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Slipping/Non-responsive Throttle in 2007 Sienna

38 messages,  Last post on Oct 19, 2009 at 11:32 AM

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What is this discussion about? Toyota Sienna, Transmission, Van

Messages Page 5 of 5

#32 of 38 Re: Slipping/Non-responsive Throttle in 2007 Sienna [ateixeira] by rivkag

Jun 17, 2008 (8:53 pm)

Replying to: ateixeira (Nov 15, 2007 9:20 am)
How about the 2008? I have this problem- took it back to the dealer twice, and they say the same-- no big deal- the computer is trying to decide which gear, etc etc.
 
Also said- no one is complaining about it....
 
To me, it feels like my old chevy van did before the transmission failed.
 
What's a girl to do?
 
Please keep me posted!
 
Rivka

#33 of 38 Re: Slipping/Non-responsive Throttle in 2007 Sienna [rivkag] by ateixeira

Jun 18, 2008 (6:59 am)

Replying to: rivkag (Jun 17, 2008 8:53 pm)
Go ahead and complain to NHTSA, click here:
 
http://www-odi.nhtsa.dot.gov/
 
If enough people complain that they find a pattern, they can force Toyota to fix it.

#34 of 38 Re: throttle response [ateixeira] by hewhohesitates

Oct 14, 2009 (7:22 pm)

Replying to: ateixeira (Nov 15, 2007 12:52 pm)
Hi there - I've experience the exact same issue with my 2008 Toyota Sienna. The hesitation in shifting at low speeds when accellerating after slowing down to turn a corner occurs intermittently but is quite noticeable. According to those in the know, this issue is absolutely linked to the "drive by wire' system, or as the service manager likes to say "it's a characteristic of the vehicle" . My mechanic friend Jamie put it best when I was expalining the issue to him the fact that Toyota Canada was unable - or unwilling - to find a fix for the problem - he said " I've got a solution - it's called a throttle cable". Nicely put.

#35 of 38 Re: throttle response [hewhohesitates] by ateixeira

Oct 15, 2009 (11:29 am)

Replying to: hewhohesitates (Oct 14, 2009 7:22 pm)
My theory is just a tad different:
 
http://townhall-talk.edmunds.com/direct/view/.f169148/7#MSG7
 
wwest was saying something about the trans waiting for revs for pressure to build up in order to shift, and there being a longer-than-usual delay when it has to downshift two gears (i.e. 4th to 2nd after a right angle turn).

#36 of 38 Re: throttle response [hewhohesitates] by wwest

Oct 17, 2009 (10:32 am)

Replying to: hewhohesitates (Oct 14, 2009 7:22 pm)
"..linked to the "drive by wire".."
 
Well, sorta.
 
Due to a transaxle design change beginning back in '98 your transaxle is NOT able to complete, QUICKLY complete, a downshift that immediately follows an upshift.
 
DBW has many positive aspects but in the instance is used as a "cover-up" for the design flaw. In instances when the downshift cannot be quickly completed DBW is used to delay the onset of rising engine torque even though you have re-applied pressure to the gas pedal.

#37 of 38 Re: throttle response [ateixeira] by wwest

Oct 17, 2009 (11:11 am)

Replying to: ateixeira (Oct 15, 2009 11:29 am)
Your ABS pumpmotor assembly includes a pressurized accumulator, holding a few ounces of pressurized brake fluid in "reserve". When ABS activates then this reserve pressure is used, INSTANTLY used, to replenish the pressurized brake fluid just previously "bled" off by the anti-lock system. The resulting sudden reduction in reserve pressure triggers the "on" cycling of the ABS pumpmotor to reactively replenish the accumulator fluid pressure.
 
Prior to ~'98 Toyota (all marques..??) automatic transaxles had this same "feature". ATF line pressure was always sustained at a fairly high level using the ATF gear type pump, a fixed relief valve (3000PSI..??) and an accumulator to provide a reserve source of ATF line pressure in situations, brief situations, wherein the ATF pump could not replenish (engine idling) the fluid pressure as fast as it was being "used".
 
Like your "old" hydraulic power stearing pump the parasitic losses of this technique are a substantial detriment to FE. The PS pressure pump must be sized to provide full functionality even in the worse case. For the power stearing pump this happens to be with the engine idling during parking, say parallel parking. Now, drive straight down the road at 70 MPH and just imagine the volume of hydraulic fluid be pumped only to be bypassed directly back into the sump having reached ~3000PSI.
 
Same for yesterday's ATF gear pump.
 
The pressure relief spring/valve has been replaced by a solenoid PWM control system such that the ATF line pressure is now under constant, "real-time", control by the engine/transaxle ECU. "On demand" ATF line pressure, no accumulator needed, nor desired.
 
So the ATF line pressure can be dropped to some minimum level, maybe even ZERO, when conditions warrant. No detriment to FE when driving along, cruising, constant speed cruising, at 70MPH....2200 RPM. No un-necessary level of ATF pump loading as you climb, accelerate, through the gears, engine ROARING to 5,000 RPM at WOT.
 
But....
 
Require a quick downshift immediately after an upshift, an upshift having resulted from a lift throttle, FULL lift throttle event.....Engine RPM has dropped to idle and there is NO reserve ATF line pressure.
 
(***1) '99 or early '00 F/awd RX300..expect transaxle failure within 50,000 miles.
 
(***2) Late '00 F/awd RX300...watch out for BURNED ATF.
 
(***3) '01 and later F/awd RX300..burned and dirty ATF in as little as 40,000 miles. Either drain/flush ATF each 15,000 miles or check ATF condition at each engine oil/filter change.
 
(***4) RX330...DBW adopted to delay rising engine torque until transaxle shifting can be fully completed. Driver's begin complaining of HAZARDOUS situations when acceleration is unexpectedly, inadvertently, delayed for 1-2 seconds.
 
(***5) RX350...Firmware revised, driver now being "watched".

#38 of 38 Re: throttle response [wwest] by ateixeira

Oct 19, 2009 (11:32 am)

Replying to: wwest (Oct 17, 2009 11:11 am)
Require a quick downshift immediately after an upshift, an upshift having resulted from a lift throttle, FULL lift throttle event.....Engine RPM has dropped to idle and there is NO reserve ATF line pressure.
 
Like in my speed bump scenario.
 
You let off the gas to slow down for a speed bump, then hit the gas after going over it, and you sense that hesitation.

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