There's a pretty clear explanation for this.
It has been almost a year since Volkswagen introduced the eighth-generation Golf – the latest version of VW's best-seller. While a lot can be said about the Golf's design, one of the great things about it is that it still can be ordered with a 6-speed manual transmission. For enthusiasts and purists, that's a huge thing, considering that only 12 percent of new models in the U.S. are offered with a stick shift.
But as with most modern cars, the latest VW Golf has an engine rev hang, which is most noticeable in cars equipped with a manual gearbox.
Gallery: 2020 VW Golf
Douglas Skorupski, Volkswagen of America, Inc.'s powertrain strategy manager, has a good explanation for this, as reported by Autoweek. According to Skorupski, the engine rev hang cuts the Nitrous Oxide (NOx) emissions of cars.
"As you pull your foot off the throttle, what we are trying to prevent is a big hunk of air getting into the chamber without any fuel. If air gets in that way, when you do reapply throttle, it creates a lean condition (a higher than 14.7:1 air-to-fuel ratio), which generates nitrous oxides or NOx. By delaying the fuel cut-off in the cylinder, we get some fuel in there with the air to keep the mixture correct and avoid the lean condition and prevent the NOx from occurring," Skorupski said in an explanation in Autoweek's report.
Engine rev hang isn't actually limited to the VW Golf. Most modern cars are equipped with electronic throttle bodies, resulting in the catalytic converter's better control of air/fuel ratio balance and improvement of throttle control. But the use of this technology also ushered in engine rev hang, especially felt in manual gearboxes since you're in full autonomy.
While it can be intrusive for some, it's good to know that engine rev hang has a positive environmental effect – no matter how marginal it sounds.