5 Causes of Engine Rough Idle In Trucks

Do you have an idea about the causes of engine rough idle? A healthy engine runs smoothly without any noise. Your engine will have a rough idle when something goes wrong. It is easy to solve rough idling if your truck experiences it. This guide will elaborate on some common causes of rough idle, which you should know and therefore fix as part of your engine maintenance.

Causes of Engine Rough Idle

Vacuum leaks or failed PCV valves are some of the most common causes of rough idle. Here are some other common causes of rough idle you should know.

Bad PCV Valve

The engine’s positive crankcase ventilation does the role of taking the unburned gases that escape from the cylinders. It moves these gases from the crankcase back to the combustion chamber so that they can be burnt completely. The PCV works within the engine and experiences pressure after being filled with the contaminants like dirt particles.

The dirt accumulation blocks it, which creates leakages and forces the air-fuel mixture to be lean, leading to rough idle.

Bad EGR Valve

The exhaust gas recirculation valve is an integral emission control device. It reduces the emission from the motor by allowing the exhaust gas to enter the intake manifold. 

The EGR should not function when your engine is idling. If it does, it will interfere with the performance of your engine. A bad EGR will stick open and lead to rough idle. At some point, it may worsen and lead to an engine stall.

Bad Spark Plugs or Wires

The spark plugs and wires are parts of the ignition system. These parts wear out as they perform their roles. The existence of the contaminants in the cylinder accelerates the rate at which they wear out. You will experience a rough idle if there is a problem with any of these parts of the ignition system. 

Blocked Air Filter

The air filter blocks dirt and other harmful particles from getting into the engine. As the air filter works, the particles accumulate on its surface and block it. A blocked air filter will not feed adequate air into the engine, leading to a rough idle. 

Replacing air filters is another maintenance task you should regularly perform to keep your engine running. You should use a high-quality air filter that does not easily clog for prolonged service.

Vacuum Leaks

The engine has several vacuum hoses. These hoses become brittle and develop cracks with time. If any of the hoses cracks, the fuel-air mixture will be lean, resulting in a rough idle. Apart from rough idle, your engine will misfire due to fault combustion in the cylinders.

The leaking vacuum supply tanks, vacuum brake booster, and intake manifold gasket can also cause vacuum leaks. When your truck has vacuum leaks, everything will run perfectly, including the RPMs, but your idle will be rough.


Engine rough idle is a problem you should not take for granted once you experience it in your truck. Shared in this guide are some of the causes of engine rough idle. If you are unfamiliar with how your engine idles, you must regularly take your truck for a mechanical check-up. Your mechanic will be able to identify various issues with your engine. 

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