Can someone explain how the variable intake cam timing works & when it kicks in

[silviasgp06]

Can someone explain how the variable intake cam timing works & when it kicks in, im trying to diagnose if my solenoid is bad.

I was under the impression that it didnt kick in(advance or retard) until a higher RPM. But my power fc shows the VTC circle fill up as soon as throttle is applied, and doesnt go away at higher RPM leading me to think its engaged the whole time. which might make my car not pull as hard in lower rpms as it should. Or am I thinking about it all wrong.

power fc menu: ECT--->SENSOR/SW CHECK labeled VTC

[Joe]

it engages low rpm, but honestly without it youll probably never know its not working.

its not like variable valve lift.

[silviasgp06]

hmm i see