The std ecu requires more than rpm to operate the VCT
The ECU checks the status that:
- engine temperature is above "min temp";
- engine temperature is below "max temp";
- load exceeds "min TP";
- speed exceeds "speed"
If above conditions are true, then it turns on at "min RPM" and off after "max PRM".
If at least one of the above conditions is/becomes false, then RPM parameter is overridden and VTC solenoid remains/turns off respectively.
On @ 1100-2000 (depending on ser I or Ser II) and off @ 5400, the on point is worth having a play with too...