Issue when taking off from standstill - jerking/lurching

[bung206]

Car is a 2006 Toyota Yaris 3DR hatchback. 4SP Automatic transmission. About 70,000 mi (110,000 km) on the odometer.

Issue I have is very peculiar.

When the car is at a standstill and I accelerate, the car will slowly start moving, then it's almost like it drops a gear and floors it. This causes the car to lurch forward.

At first I thought it was me not being used to the throttle, but no matter how hard I try I can't get it to take off smoothly. It seems intermittent. Out of ever 10 take offs from standstill, it will probably do it 5-6 times.

Once you're moving, the gearbox shifts smoothly at all other speeds.

I've owned the car for almost 1000 mi (1600 km) and it hasn't gotten any worse.

No check engine light or any warnings indicated on dash. I have scanned for errors via the OBD port and not found any DTCs stored.

Any ideas what this may be?

I know this is like asking how long is a piece of string so any help is appreciated.

[CTScott]

Have you checked the AT fluid level and checked to see if the fluid smells/looks burnt?

[bung206]

Hi,

I have not done this -- can you tell me how I can do this? Perhaps direct me to a workshop manual or similar?

[CTScott]

Hi,

I have not done this -- can you tell me how I can do this? Perhaps direct me to a workshop manual or similar?

Take a look at this post for info on how to do so:

http://www.yarisworld.com/forums/showpost.php?p=607053&postcount=8

[UberSilver]

From a start your in the lowest gear. I'm guessing it's in the accel pedal rheostat, maybe a little dirt/wear.

[CTScott]

From a start your in the lowest gear. I'm guessing it's in the accel pedal rheostat, maybe a little dirt/wear.

There are two redundant circuits on the accelerator pedal, so if one had a dead spot the ECM would detect the difference and would throw a DTC.

[bung206]

Hi guys,

I have checked the disptick for the transmission fluid. It definitely doesn't smell burnt. It is a reddish-pink color. It seems slightly overfilled though! But I need to check this again in the morning when there is proper light.

I have taken a video of this -- http://www.youtube.com/watch?v=k9XZo_niYz8&feature=youtu.be

You can see clearly. When I am stopped and I step on teh throttle, the revs climb smoothly and the car accelerates smoothly until about 1800 RPM. Then, its like I lifted off the throttle (although I didn't!) and revs drop back down to about 1100 and then it accelerates smoothly.

You can see clearly in this video.

So points of action
1. Check the transmission fluid dipstick again during dalyight
2. Capture live data thru the OBD and graph it to see what the injectors/throttle position sensor is doing at that time.

[bung206]

Okay so I've inspected the live data stream, specifally engine speed, throttle position & fuel flow in CC/min.

When I step on the gas, the engine revs start to rise until they hit about 1200, then there is a sharp drop back down to 800 or so (while the car jerks, kind of like I dropped a gear and dumped the clutch in a M/T), after which point the car accelerates smoothly. During this time, I saw that the fuel flow rate and the throttle position do not change; they are on a constant upward curve (as one would expect).

Anyone got any more thoughts on what this may be?

[CTScott]

Okay so I've inspected the live data stream, specifally engine speed, throttle position & fuel flow in CC/min.

When I step on the gas, the engine revs start to rise until they hit about 1200, then there is a sharp drop back down to 800 or so (while the car jerks, kind of like I dropped a gear and dumped the clutch in a M/T), after which point the car accelerates smoothly. During this time, I saw that the fuel flow rate and the throttle position do not change; they are on a constant upward curve (as one would expect).

Anyone got any more thoughts on what this may be?

It sounds like the torque converter in the transmission is not working properly.

[bung206]

At only 70,000? What kind of abuse could cause this? Or is it likely to just be a defective unit?

[CTScott]

At only 70,000? What kind of abuse could cause this? Or is it likely to just be a defective unit?

The only other Yaris that I have ever heard of with a failed torque converter was one that was totaled in a crash and then rebuilt. The second owner experienced the failed converter shortly after taking ownership.

[Corben]

Have you figured out the problem OP?

[WeeYari]

Have you figured out the problem OP?
8yr old thread and OP has not logged on in 3yrs. Don't hold your breath.