With Regina, the air is not "metered" ahead of the intake manifold, but the pressure is sensed.

Still, too much air passing the throttle would indeed cause the idle to be high, whether past the plate or bypassed through the idle valve. The gradual rise would occur normally in any case where the air is not getting regulated by a warm-up response of engine control feedback, such as the RPM-adjusted idle valve.

So, the approach I'm recommending is, first, determine if the ECU is aware that the idle speed needs regulating, or in other words, is the computer brain aware you're not holding the accelerator pedal down. Then second, if it is aware, is the brain able to do something about it, i.e. limit the air it sends around the throttle plate that is senses is closed.

Another, easier method to determine whether the TPS is working, since you are not getting erratic response, is to simply disconnect it. If it is unplugged, the ECU is going to assume the throttle is open. So if your symptom doesn't change when you unplug the TPS -- that is if it still gradually revs up -- you have your #1 part of interest.

--
Art Benstein near Baltimore

You can easily judge the character of a man by how he treats those who can do nothing for him. ~Malcolm S. Forbes