When your car experiences rough idling, your engine may stall, vibrate, or shake while it’s running. This will make your overall driving experience difficult and you’ll likely bounce a bit in your seat.
When the engine is idling, there’s typically a misfire that you can feel simply by holding onto the steering wheel. Additionally, your engine’s RPM will be higher than normal when the vehicle is idling.
The RPM usually returns to normal when you accelerate the vehicle, but increases again after stopping. This is certainly not a normal situation.
Reasons for Rough Idling or High RPM
If you’re experiencing rough idling or your RPM is high, there are several reasons why this might happen. It’s not always easy to diagnose the cause because there are so many factors involved here.
Here are the top 5 causes that a mechanic would look for.
1) Bad Spark Plugs
If you have bad spark plugs because they’re worn out or damaged, this could cause the engine to idle roughly. Remember that spark plugs send an electrical current into the internal combustion chamber to ignite the fuel-air mixture.
If the spark plugs are bad, the electrical current won’t be sufficient for ignition. This will result in irregular combustion of the air/fuel mixture, leading to rough engine idling.
2) Vacuum Leak
There are many hoses that help supply both fuel and air to the internal combustion chamber. A very common cause of rough idling is a problem with a vacuum hose in the vehicle. The hose could be damaged, loose, or worn out, creating a leak.
This could cause an abundance of air mixing with the gasoline, which would result in misfiring. Then, the result would be a car that idles roughly or has higher than normal RPM.
3) Carburetor Problems
Carburetors were previously used in vehicles before the invention of fuel injectors. Perhaps you have a vehicle that still contains a carburetor.
If so, the carburetor itself could have problems causing rough engine idling. A warning sign of this would be if your exhaust smoke turns black.
4) Dirty Fuel Injector
Fuel injectors are the modernized way vehicles route fuel into the internal combustion chamber. The only thing is that these fuel injectors can get dirty or clogged over time.
If you don’t use gas additives or fuel injector cleaners regularly, there’s a good chance you’ll get a dirty fuel injector at some point. This will cause your car to idle poorly. You may also see your gas consumption take a dive.
5) Clogged Air Filter
The engine needs air from outside to mix with the fuel in the internal combustion chamber. There’s an air filter that prevents debris from the air from entering the chamber.
But if this air filter is dirty or clogged, there will be less clean air passing through it. This will cause the engine to idle roughly.
Things to Remember
Your engine should normally reach about 700 RPM after starting the vehicle. If it’s lower or higher by a few hundred RPM and you’re experiencing one or more of the issues listed above, you’ll want to diagnose the problem immediately.