Cutoff at low RPM during gentle acceleration - Yaris Verso 1.3 VVTi

[jackmilas]

I get short engine cutoff which causes jerky acceleration.
It happens at low RPM, around 1200, on each gear.
The best way to present the issue is to try to drive over a curb from complete stop. I have a steep entry to my garage, you can see in the video, where I keep the throttle gently and steadily pressed in: https://www.youtube.com/watch?v=Ll7Rh31lpc8

Other than that the car runs super smooth but there's a problem with fuel economy. Car's display shows 6.5l/100km average but real consumption is 8.5l/100km (calculated from distance driven and fuel tanked).

I exchanged Mass Air Flow sensor with my Prius but even with MAF sensor completely disconnected the issue stayed there. I ordered a new front O2 sensor but I get a feeling it will not sort it out.

Would anyone be able to help me before I go to Toyota dealership and before I spend too much money there?

[Bluevitz-rs]

Are there any codes?

Can you still drive the car or does this only happen under light throttle application?


Sent from my iPod Touch

[jackmilas]

Are there any codes?

Can you still drive the car or does this only happen under light throttle application?


Sent from my iPod Touch

There are no codes when I check it with iPhone app OBD Fusion.

I can still drive the car. It happens only at light throttle at around 1200RPM and under a load. I can't reproduce it on neutral. In normal use it just gives me one or two "jumps" during light acceleration from complete stop. 1-2 out of 5 times it won't happen at all.

My guess is that ECU cuts the fuel off because some specific sensor values are met. Things that didn't help:

- disconnecting MAF sensor
- disconnecting both O2 sensors
- 98 octane fuel instead of 95
- injector cleaner fluid

The car has 140k kms, 15 years old.

[Bluevitz-rs]

Can you see the reading of the throttle position sensor?

[jackmilas]

Can you see the reading of the throttle position sensor?


I just checked it. My default (throttle off) position is 11.8% and the engine cutoff happens at around 17%. Gentler or harder acceleration doesn't produce the problem.


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[Bluevitz-rs]

It's the reading steady and smooth all the way through the full range?

[jackmilas]

It's the reading steady and smooth all the way through the full range?

It is.

[Bluevitz-rs]

have you tried unplugging the TPS?

I can't think of anything else that would cause a light load hesitation at a certain throttle angle like what you're experiencing.

[Bluevitz-rs]

Both Intake air and Coolant temps are reading normal?

[jackmilas]

have you tried unplugging the TPS?

I can't think of anything else that would cause a light load hesitation at a certain throttle angle like what you're experiencing.

I'll give it a go tomorrow.

Regarding temperature question - yes, they read normal.

But I forgot to add that the problem occurs after "cold engine" warning light goes out. When the light is on there is no jerky acceleration. As soon as the light disappears, the problem appears.

[Bluevitz-rs]

Ok check and see if the problem only occurs when the Fuel system is in Open Loop or Closed Loop. Therefore it's a sensor problem somewhere.

[jackmilas]

Both Intake air and Coolant temps are reading normal?

I looked more carefully into intake temperature. Today the outside temperature was -8C. The intake air temperature was showing values between -1C and 1C.

[jackmilas]

have you tried unplugging the TPS?

I did it today. No change.

[Bluevitz-rs]

I looked more carefully into intake temperature. Today the outside temperature was -8C. The intake air temperature was showing values between -1C and 1C.

that seem right.

I'm running out of ideas...

There is a code set every time you unplug a sensor and run the car right?

[jackmilas]

that seem right.

I'm running out of ideas...

There is a code set every time you unplug a sensor and run the car right?

Yes, there was a check engine light and throttle sensor error.

[Bluevitz-rs]

It's an automatic I'm assuming from the video...

I'm wondering if it's a transmission problem of some kind.

[jackmilas]

It's an automatic I'm assuming from the video...

I'm wondering if it's a transmission problem of some kind.

Can the transmission send "cut fuel" message to the ECU in those specific conditions?

- it happens only at a specific throttle position (even with throttle sensor disconnected)
- it happens only at low RPM range, around 1200-1400RPM
- it happens only when the cold engine warning goes out
- it happens at every gear

Today I'm replacing front O2 sensor and I'll report back if there has been any change. Some people say that 16 year old car with 140k kms will benefit from replacing O2 sensor in better fuel economy anyway. For some reason I am one of top Yaris Verso fuel consumers despite that I drive very economically: http://www.spritmonitor.de/en/detail/725585.html

The car is showing average fuel consumption at 6l/100kms (I reset it at each full tank) and in reality the car burns 8l/100kms. Perhaps both issues have the same root cause?

[Bluevitz-rs]

Yeah a lazy front O2 sensor can cause poor fuel economy. It happened to me.

Have you tried disconnecting the battery and letting the computer reset?

I keep thinking it TPS related because I feel like somehow the ECU thinks the engine should be idling and sees a "fast" idle speed and cuts fuel to bring it back to idle.

[jackmilas]

Success!
New front O2 sensor improved the situation a lot!
But occasionally I get this hesitation, so it's not solved entirely yet. Perhaps it would happen 4 times out of 5 before, now it is once out of 5 and much smoother / gentler.

Could the rear O2 sensor bring more improvement / solve it entirely?

I didn't disconnect the battery after replacing front O2 sensor. I did it now and I'll report back if there's any change.

PS.: Previously I unplugged the battery a few times - there was no change then.

[Bluevitz-rs]

The rear O2 is on there to affect Long Term Fuel Trim and monitor the Cat.

[jackmilas]

I ordered MAF sensor yesterday. This is one of the oldest cars on this forum so I guess other people will benefit from my experiments :) I'm going to install it within a few days and I'll report back.

[jackmilas]

I got P0420 code today.
I will be replacing rear O2 sensor as well and I'll report back.

The car is much nicer to drive after changing front O2 sensor.

[Bluevitz-rs]

Take a reading of the O2 sensor first before throwing parts at it.


Sent from my iPod Touch

[jackmilas]

Take a reading of the O2 sensor first before throwing parts at it.
Sent from my iPod Touch

I understand the logic of checking everything before making changes. I decided this car is old enough to change both O2 sensors and the MAF sensor, because they wear out by their nature. It costs me less than 200 EUR and I will probably recoup that in better fuel economy within a year.

Now, the front O2 sensor made a huge difference. I just finally took it outside the city and I drove fast on a motorway. Noticeably more power and from looking at fuel gauge and distance driven I get a feeling that fuel economy might somehow get closer to what the car's economy display is showing (~6.5l/100km).

... more to follow :)

[Bluevitz-rs]

I guess a 15 year old car doesn't owe you much now.

New parts shouldn't hurt if you have money to spend on them.

[jackmilas]

The car drives great, the jerk most of the time is gone but it still happens sometimes. I was thinking that it wasn't there before I changed oil and oil/air filters in November. There was synthetic 10W40 (I don't remember the make) before, I replaced it with Castrol Magnatec 10w30. Perhaps I should change it back to 10W40? Or maybe I should put original Toyota SAE 5W30 there?

[Bluevitz-rs]

I'm always sticking with 5-30. Unless your racing or live in a very hot climate you don't need a different grade.

[jackmilas]

Changing the sensors helped to decrease the severity and frequency of jerky starts under light acceleration at low revs. But I'd like them gone completely. Would any of the below cause the issue?

- dirty fuel filter
- worn out fuel pump
- blocked air vent to fuel tank

[Bluevitz-rs]

I forget. Did you confirm your TPS is around 10-12% at idle. And it indeed moves with the crack of the throttle and is linear.

[jackmilas]

I forget. Did you confirm your TPS is around 10-12% at idle. And it indeed moves with the crack of the throttle and is linear.

My default (throttle off) position is 11.8% and the engine cutoff happens at around 17%. Gentler or harder acceleration doesn't produce the problem.
Disconnecting TPS doesn't make any change to the issue.

[Bluevitz-rs]

And if you hold it there it just keeps surging

[jackmilas]

Here is something that points me towards VVTi problem:

VVT-i is disabled when the "COOL!" light on your dash is on.

[Bluevitz-rs]

Ok then simply unplug the VVTi on the engine and see if the problem goes away.

[jackmilas]

Ok then simply unplug the VVTi on the engine and see if the problem goes away.

I disconnected Oil Control Valve which I understand controls the VVT system. The problem is completely gone.
Since the the VVTi is controlled hydraulically using engine's oil my guess of incorrect oil might not be entirely missed. I am going to drive it without VVTi for a while and I will investigate what oil might be suitable.

[Bluevitz-rs]

If that's the case, there's a chance there's a clog in the passages of the VVTi oil flow to the variable cam. You can probably pull the valve cover and the cam cap over the pull side of the cams to expose the the oil passages. With the oil control valve out, you can blow it out with compressed air and some brake cleaner.

But before that you'd have to check the signal from the cam sensor to make sure it isn't false.

[sarap]

wow so much knowledge gained between the last two pages in this thread !
OP hope everything works out for you !

[jackmilas]

This article helped me to understand the concept of VVTi: http://www.drivenracingoil.com/news/dro/training-center/articles/variable-valve-timing-places-extra-demands-on-motor-oil/

Obviously foam is a poor lubricant, and it is an even worse hydraulic fluid. The air can be compressed, and a good hydraulic fluid should be basically incompressible. If your motor oil foams, you could be in trouble.

After reading the above I thought that VVTi might get too little oil to function and some air bubbles could be impeding its operation. I checked the oil level this morning. It was the same as when I changed the oil 3000kms ago to Castrol Magnatec 5W30 A3. On the dipstick it was at around 80% between L and F. I didn't think about filling it to 100% at the time. I added around 200ml today so it went up to 100% and I reconnected Oil Control Valve. It did one little jerk when I accelerated for the first time, but then I could not reproduce the problem anymore. So it seems I should keep the oil level at FULL position on the oil dipstick to make the VVTi function properly. That explains why the problem appeared exactly after last oil change.

This problem would probably go completely unnoticed in a car with manual transmission because a driver would compensate the problem releasing the clutch at slightly higher revs.

Summary:

- my problem was related to VVTi
- adding more oil to 100% on the dipstick cured it
- replacing O2 sensors with new ones made the engine work considerably better (more power) and made the VVTi symptoms less annoying
- replacing MAF Sensor didn't make a noticeable difference in the way the car works

[jackmilas]

It was an interesting experience to drive the car with VVTi disengaged. The difference was much less torque at lower RPM. It helped me understand what difference it makes.

[NYC-SE]

I think it is simply a coincidence that your symptoms stopped after adding oil. I suspect they will reappear. Low oil level should make no difference, it is the oil pressure that matters. Now if the oil level was EXTREMELY low, it is possible that the engine would lose oil pressure. But at that point a faulty VVTi would be the least of your problems.

[tmontague]

^agreed

[jackmilas]

I think it is simply a coincidence that your symptoms stopped after adding oil. I suspect they will reappear. Low oil level should make no difference, it is the oil pressure that matters. Now if the oil level was EXTREMELY low, it is possible that the engine would lose oil pressure. But at that point a faulty VVTi would be the least of your problems.

If the problem reappears I will update this thread. Currently the engine makes absolutely no hesitations, like before the oil change in November.

Some important point that will be useful for other users in future: If you have a problem that shows itself only after the cold engine warning light turns off, it is very likely that it is related to VVTi.