What Causes Rough Idle At Low RPM? (5 Possible Causes)

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What causes rough idle at low RPM? The most common causes include faulty or clogged injectors, bad filters, or a failing sensor. Your car is not meant to rough idle at any time; hence, if that happens, you should try to fix the faulty component as early as possible.

Rough idling at low RPM simply means the car shakes or bounces when you’re not even at top speed. Well, even when driving at top speed, a sound engine would not rough idle. Hereunder, we have explained the common reasons why a car may rough idle at low-speed levels.

What Causes Rough Idle At Low RPM?

1. Bad Spark Plugs

The spark plugs are an important part of the engine, if anything happens to them, the engine would suffer the consequence. Actually, spark plugs ignite fuel in the engine so the engine can perform its duties.

When the spark plugs are clogged or damaged, it can cause a shortage of fuel inside the engine; hence, the rough idling at low RPM.

2. Clogged Fuel Pump or Filter

If your engine’s fuel pump or the fuel filter is blocked, it can cause rough idling because the engine would be in shortage of fuel. Fuel filters can get clogged up due to debris suctioned from the gas tank when you were running low on gas/fuel.

The fuel pump can be affected by quite a number of factors, and when that happens, it reduces fuel inflow to the engine, which may be the cause of the rough idling. Having the fuel pump and filter replaced isn’t really that expensive.

3. Faulty Fuel Injectors

What Causes Rough Idle At Low RPM

Fuel injectors are also part of the fuel delivery system that sends fuel from the gas tank to the engine. Hence, any issue with the fuel injectors would lead to a fuel shortage in the engine, which can also cause rough idling.

4. Vacuum Leaks

There shouldn’t be any leaky spot in your vehicle’s engine bay. Vacuum leaks provide space for air to get into the engine; thus, affecting the air-to-fuel ratio. With too much air inside the engine, the engine is likely to constantly misfire, and also rough idle at low RPM.

The solution is to check the vacuum system, inspect all the hoses, and replace the worn-out ones. Ensure that all leaky spots are fixed to prevent too much air from penetrating into the engine.

5. Failing Sensors

A car works with many sensors; oxygen sensors, airflow sensors, and others. These sensors are often overlooked, but they play a vital role in determining the air to fuel mix ratio. However, these sensors can fail due to several reasons, including excessive wear due to intense pressure.

Apparently, a faulty or failing sensor would affect the air-to-fuel ratio, which in turn, can cause your car to rough idle at low speeds. To find out the exact faulty sensor, you need to troubleshoot your car using an OBII scanner or any other car troubleshooting tool.


So, what causes rough idle at low RPM? The issue is due to a failing (or already failed) component. The common components that could cause this scenario include clogged filters, fuel pumps, sensors, and bad spark plugs.

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