Stock '13 V6 manual here. And I don't know anything about modern engine management stuff. It probably doesn't matter, but 3.31 rear.

I can put the car into 1st to 4th gear, and without my foot on the gas, the engine settles to ~500RPM (always the same RPM in each gear) and drives smoothly and quietly without lugging. At different speeds of course. I can't do that at such a low RPM with my foot on the gas in 4th gear, maybe not even 3rd (I forget now), no matter how lightly I touch the gas. How does it do it, technically speaking? Thanks.

This is actually useful in some heavy traffic here, also on a so-called "paved" road I regularly use that is very narrow and often has lots of people walking along the sides.

 

It's not really engine management... except in the idea of the car wanting to keep the engine running, that's all.

You're lugging it, but I get what you're doin'. And so if you put it in the proper gear at the right speed, yep, it'll stay running at 500RPM... but it's not liking it, it's not near as efficient, and the power isn't as available as at 750 or 1000 RPM to get movin'.

But it's just the engine computer saying "LIVE, DANGIT, LIVE!!!"

 

^ Well, not really. I've been driving manuals for several decades, so I know lugging. It isn't lugging, it's smooth and silent, and that's why I'm asking the question. Anybody can make their engine lug and stall etc., the car isn't drivable in 4th gear at this low RPM/speed. How does it do it without lugging at such a low RPM in 4th gear, because I can't? Touch the gas and you'll immediately lug or stall, don't touch it and you can drive for miles...

So: how is it keeping the engine running?

There sometimes is a "benefit" of being able to drive at a very slow speed without having to continually gas/brake/clutch. It is pretty convenient around here sometimes. Just try driving for a while with your foot on the gas in 1st gear at 500 RPM, about as low/slow as you can go, and even that slowness is an "effort" to maintain (in traffic, say) for any significant time.

The efficiency gauge bar is bottomed-out while doing it, barely shows when there's regular driving also on the same graph. Though in reality it can't be that proportionately efficient, I'm just saying it's apparently not pouring gas into the engine to do it. The engine is barely audible, I have my windows open, and this isn't a particularly quiet engine either.

I hope it's clear that I'm doing this because I want to drive at a slow speed (traffic jammed, good scenery , etc.), so obviously acceleration etc. is not a point. That's how I found out about it long ago, but I never tried it in 3rd or 4th gear until the other day, I wouldn't have imagined it would work because that's getting "crazy", right? 5th gear is the next experiment lol.

 

I have done that in a parade. I didn't pay any attention to the gear, but I suspect it never shifted up out of first.