This does not conform to ngspice syntax, even if it may be working (see ngspice manual chapter 2.9.1, here missing ’ ’ or { } ).
And what is ‘wiper’?
You may find some potentiometer models at Simulation examples for KiCad8/Eeschema/ngspice.
Edit: Have not heard from you for some time. Attached you will find my vco project
VCO_briscoe.7z (14.6 KB).