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

[jackmilas]

This article helped me to understand the concept of VVTi: http://www.drivenracingoil.com/news/...-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