Engine "surge" during constant speed

[John Lenin]

2009 Yaris 2 Dr. H/B automatic, 41,000kms (25,477 mi)

Have noticed that while driving at a constant speed at approx. 60-65kph (30-40mph) on a level road or slight downgrade with tranny in the "D" drive mode, that my tach will show revs approx. 1200-1500 RPM and then suddenly drop to 1000 RPM or slightly less, making the car "surge" like under engine-braking. I don't feel like I've backed off the throttle but revs climb back up again to original level once I do apply a bit more toe to the gas pedal. This happens intermittently and mostly if I am travelling along a long stretch of level road (or slight downgrade) at as I said, a constant speed.

Car is a recently purchased Lease Return to replace my previous 2008 Yaris H/B 5-spd which I could no longer drive on account of a broken left leg ... which I was very happy with BTW ...

All comments welcome and appreciated!

[IllusionX]

The automatic gearbox will downshift on a downhill if you are slow enough to not stay in 4th. L

[John Lenin]

OK ... that kinda makes sense to me ... though, my (ex) wife and I once each owned a couple of 2005 Toyota Echo's with auto-trannys that did not exhibit this behavior? ... But the Echo auto-boxes seemed slightly different with an O/D on/off switch on the side of the gear selection lever ... we always kept the O/D on.

BTW, if the Yaris auto-trans downshifts to 3rd on a downgrade because speed is not enough to stay in 4th, shouldn't the revs increase instead of suddenly decreasing? ... in a manual trans a downshift fr. 4th to 3rd at approx. 60kph would result in increased revs once the clutch is re-engaged ...

Thanks for the reply!

[IllusionX]

Yeah, I'm a bit intrigued by the losing rev part.
Does it do it on a flat surface too at the same speed? I wonder if it could be something about the pedal

[John Lenin]

Found this with a Google search;


Jumping to conclusions


I purchased a Toyota Yaris last year and was told it was an automatic, but it seems not to have a conventional auto transmission. I am 81-years old and always used to drive automatic Toyotas. They were fine, but the Yaris sometimes feels strange, as though it can’t decide whether to go up or down a gear.


CH, via email


Yaris automatics from 2006 to 2012 were automated manuals. These are standard manual gearboxes and clutches operated by a system of servos and electric motors to emulate a driver changing gear. One peculiarity is that they damp the throttle on upchanges to prevent damage to the transmission. If the driver tries to overcome this by pressing the accelerator harder, then progress can be spoiled by a series of jolts. They do require a little acclimatisation.

[IllusionX]

^This doesn't apply in North America.

[John Lenin]

Thanks for the heads-up ... autobox tranny does seem to exhibit the "hunting for the right gear" behavior from time-to-time though ...

[John Lenin]

OK, found this on the Interweb ... Edmunds Discussion form about the Yaris auto-tranny. This quote describes 'zactly what I've experienced;

When I take my foot off the gas, the engine sometimes slows down jarringly, like the car just hit a patch of wet sand. And sometimes it even feels like it surges back to normal again. This doesn't happen all the time when I take my foot off the accelerator but I notice it the most when I am in stop and go traffic and accelerate a little then take my foot off the accelerator. Sometimes I even feel it when I still have my foot on the accelerator but not giving it much gas. Like the engine surges down quickly and sometimes even back up again

Here's the link to the Edmunds Forum;

http://forums.edmunds.com/discussion/6597/toyota/yaris/new-yaris-problem-a-lemon

Some follow-up posts seem to indicate that the described condition is normal?

Toyota has been programming their transmissions to do this for many years now.

1. In the morning first thing, the transmission stays in lower gears to make the engine rev more and warm it up faster. It's an emissions thing. Trust me, if you rev it hard enough (like if you need to go freeway speed) it will eventually upshift.

2. It has "grade logic" for downhill - my Matrix auto had this. Depending on sensors under the hood that judge the grade and the amount you step on the brakes, it will downshift and hold the lower gear to provide some engine braking until the grade changes, or you step on the gas for longer than a second or two.

[IllusionX]

Decelerating on a downhill is not constant speed.

[John Lenin]

Decelerating on a downhill is not constant speed.

LOL! Obviously, deceleration is NOT constant speed!

Am curious to know if the operating conditions described in the Edmunds Forum for the Yaris P-R-N-D-3-2-L auto tranny are normal ... and if this "grade logic" referred to above is real or not? The auto trannys in both of the Echos I've owned in the past did not behave "oddly" whatsoever?

[andro marcello]

maybe your oil is to "thick", or the valve timing controler selenoid is stuck?. Change the oil to the less viscous (eg. 5w-30) and cleand the valve timing selenoid thoroughly. You can use MAF cleaner.

[xdarkxfirex]

The yaris has somewhat of a naturally funky acting tranmission. We bought a lease return last year from a private dealer with around 122k, and I put around 30k on it. When cold, it takes a bit longer to shift to 3rd from second. Since it only has 4 gears, I assume that it could be causing somewhat of a problem. When I go uphill or downhill, I find myself jumping between 3 and 4 alot. I can even manually change it many times from 3 to 4.

A few months ago I did a drain and fill with full synthetic atf at around 50k. No difference, and there wasnt metal shavings or anything. I believe it's just the design. You shouldnt worry to much about it. If you get high or low revs, just give it a little more or less gas or change it manually