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Hello and thank you for using Just answer! I'm Billy and i will assist you with this. Feel free to ask if you need any further info.
This basically is a problem caused by the VVT system (variable valve timing).
The VVT system essentially would retard and advance the camshaft, to get the optimal valve opening throughout the whole range (RPM)
I will include the detailed description and operation of the system, as well as the check procedure, so you check accordingly:
click here for the details