Idle Mode: Why Electric Cars Are More Efficient Than ICE Cars

Have you ever noticed the difference between sitting in a gas-powered car and an electric vehicle (EV) when the car isn’t moving? It might not seem like a big deal, but what happens at idle - when you’re stopped at a red light or waiting in traffic?

Idle Operation in ICE Vehicles

In an ICE vehicle, the engine must maintain a baseline speed, known as the idle RPM, even when the vehicle isn’t moving. This idle speed typically ranges from 600 to 1000 RPM, depending on the engine type and load demands. This seemingly small figure carries significant implications:

Maintaining idle RPM requires continuous combustion.

The throttle valve remains slightly open, allowing a controlled air-fuel mixture into the cylinders. Even when the engine is “resting,” fuel is burned to overcome internal resistance caused by moving components such as pistons, crankshafts, and valve trains. This steady consumption of fuel is an unavoidable aspect of ICE operation.

Additionally, ICE engines must supply power to auxiliary systems such as the alternator, power steering, and air conditioning. To meet these demands, the engine’s idle RPM is carefully calibrated. However, this adds to the overall energy consumption and mechanical strain on the engine, even when the vehicle isn’t in motion.

Another notable aspect of idling in ICE vehicles is mechanical vibrations. The reciprocating motion of the engine’s pistons generates vibrations that travel through the vehicle's structure.

Idle in Electric Vehicles: Zero RPM, Zero Energy Loss

Electric motors fundamentally change the concept of idling. Unlike ICEs, electric motors don’t need to maintain a rotational speed when the vehicle is stationary. No Idle RPM is one of the most significant differences. Unlike ICE engines that must maintain a baseline RPM, electric motors operate only when a driving current is applied.

At idle, the motor remains effectively inactive, consuming negligible power.

The only energy draw comes from low-power systems like infotainment or climate control, meaning there is no mechanical energy wasted since the motor doesn’t rotate.

Another key advantage is eliminating vibrations. Unlike ICEs, which rely on reciprocating motion, electric motors operate via smooth electromagnetic fields. This fundamental difference ensures that electric motors produce no perceptible vibration, even at rest. The result is a quieter, more comfortable experience for passengers and reduced structural wear on the vehicle.

When it comes to energy management, thermal efficiency plays a critical role. At idle, the motor is effectively at rest, and heat generation is limited to minor resistive losses in auxiliary electronics. This contrasts sharply with ICEs, where a significant amount of energy is wasted as heat during idle.

Perhaps the most striking feature of electric motors is their instantaneous torque availability. While ICE engines need to ramp up their speed to produce usable torque, electric motors deliver peak torque instantly from zero RPM. This capability is particularly beneficial in stop-and-go traffic, where rapid response and energy efficiency are crucial.

Summary

The next time you’re in a car that’s sitting idle, pay attention to what you hear and feel. If it’s an ICE vehicle, you’ll notice the engine humming away. But if you’re in an EV, you’ll enjoy the silence and efficiency that comes with a motor that doesn’t need to run unless you’re moving.

It’s a simple difference, but it speaks volumes about how far car technology has come—and where it’s headed.

Here’s a clear and concise table comparing ICE engines and electric motors at idle:

Sumeet Singh, PhD - Product Manager for eMotor Electromagnetic Simulation at EMWorks Inc., Montreal