If you can run car at idle on ramps, start car let idle.
From under car observe vnt actuator arm position, should be pulled in toward s radiator( max spool 75% )and the arm should be resting against the stop screw(not sure if better seen from above to see if resting against screw)
Now pull off the silcone pipe going to actuator, vnt rod should now push out towards engine approx 10mm and stop(min spool position) put pipe back on actuator, and it should pull back in fairly quickly back to the stop screw.
If it does not do this test vacuum on the pipe, you need -600mbar to reach the stop screw.
If less than this you should look to vnt solenoid or leaks on vac pipework( bypass solenoid to test?)
Or actuator diaphram issue or sticking
Or vnt vanes or ring sticky or seized.
If you can get a pretty big syringe or vac pump you can connect direct to actuator and exercise mechanism(engine can be off for this, just see rod move smoothly)
Heres mine on bench, pulling with syringe approx half way(bigger syringe or 2 td together will reach stop pin.
vnt operation for youtube.avi - YouTube
If you have no gauge to measure vacuum a garage may lend you one as test would take seconds, gauge connected to silicone hose off actuator)