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Old 02-19-2016, 03:52 AM   #37
jackmilas
 
Drives: Yaris Verso 1.3 2000 automatic
Join Date: Nov 2015
Location: Poland
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This article helped me to understand the concept of VVTi: http://www.drivenracingoil.com/news/...-on-motor-oil/

Quote:
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
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Old 02-19-2016, 04:57 AM   #38
jackmilas
 
Drives: Yaris Verso 1.3 2000 automatic
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Posts: 33
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.
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Old 02-19-2016, 01:14 PM   #39
NYC-SE
 
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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.
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Old 02-19-2016, 01:34 PM   #40
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^agreed
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Old 02-19-2016, 03:18 PM   #41
jackmilas
 
Drives: Yaris Verso 1.3 2000 automatic
Join Date: Nov 2015
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Quote:
Originally Posted by NYC-SE View Post
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.
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