I've driven in mountains (I'm actually in the mountains, with snow on the ground, even, right now) and for 15 years drove manual (I sometimes miss it, but mostly do not, in the same way that I run Debian now and can't be bothered to run a distro like Gentoo anymore), but I literally never thought of pressing the gas pedal as "regulate the intake manifold". I honestly don't even know what an intake manifold is, though I'm sure if I cared enough, Wikipedia would tell me.

Certainly my understanding of it is a bit more nuanced than simply "accelerate", but ultimately.... "press pedal harder, car moves faster" is... fine? Sure, you have to consider road conditions and (if driving manual) your current gear, speed, RPMs, etc., but... I dunno, I still think "press pedal harder, car moves faster" is a useful mental model to have, to some non-zero level of approximation.

Put another way: if I were to think of all the details of what the accelerator of a car actually does under the hood every time I pressed it, and consider the implications of it and allow that to inform how I press the accelerator, I would have precious little time to actually drive the car... like, the things that actually matter, like steering and staying on the road and avoiding other cars and people and whatnot. When I press the accelerator, I think about the effect it's going to have on the car. And I have a good idea of what effect it's going to have based on my experience driving that car (or any car, really). Not based on any knowledge -- knowledge that I lack! -- of what pressing the accelerator actually does.