Why do cars shudder at low revs?

[Pushkin]

@matt

Truth is, getting a modern car to lug the way I described is pretty difficult. They either run, or they stall. But back before the days of engine management, egr valves and anti-knock sensors, let the revs get too low and they’d lug as I described. Clutch fully engaged. “Whiplash inducing” is an exaggeration, but it’s that sort of motion

I was describing the shuddering from driving both my parents’ cars, with reasonably modern engines.

I get what you’re talking about when I’m creeping along in traffic and the queue briefly moves too slowly for me to apply the accelerator but above stall or “lugging” speed. As Death Ray, noted, there’s an unbalance made between throttle and clutch that produces the effect.