True, idling is wasteful, but at the same time “spinning fast” does not necessarily equate to “high energy consumption.”

The CPU fans in my computer spin at about 1000 RPM all day long but that doesn’t mean they’re consuming a lot of electricity.

Well.. as so many things in engineering: it’s a tradeoff. Mechanically, it’s also very important to let the engine warm up and cool down before and after heavy load. Primary reasons for warmup are that the oil is more fluid on higher temperatures and metal is also less fragile when 50 or so degrees above freezing. Cooldown is especially important on turbo engines as the turbo on hundreds of thousands revs per minute and high temperature needs oil to be pumped through the bearings. If you turn it off after heavy load on engines that do not keep the oil running after motor shutdown, there is a chance that oil burns and gets stuck in the bearings, degrading performance or worst case breaking the turbo.

At idle, it doesn't take that much fuel to keep the engine alive. Idle stops are more important for noise abatement and local toxic exhaust gas emissions - a lot of exhaust gas treatment depends on the exhaust gas having a minimum amount of thermal energy.

The downsides of idle stops are, however, that they tend to put a lot of load on the engine, especially from the lack of oil pressure at the very few first strokes [1], and that the low temperature deposits all kinds of gunk in the exhaust pipework instead of transporting it outwards.

If you run an engine with idle stop, it really really is important to properly take care of the engine, including preventative maintenance and regular oil changes.

[1] That is even more of an issue in large engine blocks, hence that high pitched noise you hear from ships and locomotives for a while before they start up - that is an ancilliary oil pump, priming the entire oil pipework until all air is gone and full oil pressure is present at all ports in the system.

But combustion engines go also much faster than 9000 RPM; afaik bike engines can reach 18000 RPM or more.

You’re correct, would be equivalent to 150Hz. I was curious too since my monitor is 360Hz :)

Not pedantic enough because we have 500Hz monitors already. Don’t think that’s the point the author was trying to make though.