In a lot of ways, electronic throttle bodies are very good. One perhaps unexpected benefit of ditching a traditional cable-operated setup is a potentially more linear torque curve since response can be tuned however the engineer desires.
As Engineering Explained, erm, explains, electronic units are also better for efficiency, but there is a side effect of this - rev hang. Heavy flywheels are usually blamed for this, but on modern manuals, rev hang is usually down to a deliberate choice in the way the throttle body is set up.
Jason takes us through in-depth using his trusty whiteboard, but to summarise, it’s all down to the wastage associated with suddenly shutting off the throttle. Bleeding it off slowly is much more efficient, but that comes at the cost of fast gear shifts feeling much less satisfying.
The problem is often worse with direct port injection, where there’s usually a little fuel still making its way into the combustion chamber when the throttle closes. A slower closure can ensure the fuel/air mixture isn’t too rich, lowering emissions and fuel consumption.
We shouldn’t be too mad about this - manufacturers are up against it when trying to comply with ever more stringent emissions regulations, so if there’s a way to make less nasty stuff belch out the tailpipe, they’re going to want to do it. Plus, some cars have more aggressive mapping on sport/dynamic modes that allow for faster closure of the throttle, cutting down on hang.
Is rev hang an issue for your car?