5 Causes of a Rough Idle or High RPM in Your Car

When your car is experiencing a rough idle, your engine may chug, vibrate, or shake while it’s running. This will cause your overall driving experience to feel rough and you’ll likely be bouncing a little bit in your seat from it.

When the engine idles, there will usually be a misfire that you can feel just from holding onto the steering wheel. Furthermore, the RPM of your engine will be higher than normal when the vehicle is idle.

The RPM will usually go back to normal as you accelerate the vehicle, but will increase again after you stop. This is definitely not a normal situation.

Reasons for a Rough Idle or High RPM

If you are experiencing a rough idle or your RPM is running high, then there are a variety of reasons for why this could be happening. It is not always easy to diagnose the cause because there are so many factors involved here.

Below 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, then it could be causing your engine to be idling rough. Remember that spark plugs are what send a current of electricity into the internal combustion chamber to ignite the mixture of fuel and air.

If the spark plugs are bad, then the electrical current won’t be sufficient enough for the ignition. This will cause the fuel and air mixture to burn inconsistently, which will result in rough idling engine.

2) Vacuum Leak

There are a lot of hoses that help deliver both fuel and air to the internal combustion chamber. One very common cause of idling rough is a problem with a vacuum hose in the vehicle. The hose could be damaged, loose, or worn out, creating a leak.

This could result in an abundance of air mixing with the gasoline, which would result in a misfire. Then, the result of that would be a car that is idling rough or having a higher than normal RPM.

3) Carburetor Issues

Carburetors were previously used in vehicles before fuel injectors were invented. Perhaps you have a vehicle which still has a carburetor in it.

If so, the carburetor itself could be having issues resulting in rough idling of the engine. A prewarning sign of this would be if your exhaust smoke becomes black.

4) Dirty Fuel Injector

Fuel injectors are the modernized way in which vehicles deliver fuel into the internal combustion chamber. The only thing is that these fuel injectors can get dirty or clogged after a while.

If you are not using gas additives or fuel injector cleaners on a regular basis, then there’s a good chance you’ll get a dirty fuel injector at some point. This will result in your car idling poorly. You could also see your gas mileage take a nosedive as well.

5) Clogged Air Filter

The engine needs air from the outside to mix with the fuel in the internal combustion chamber. There is an air filter which prevents debris from the air from getting into the chamber.

But if this air filter is dirty or clogged, then there will be less clean air passing through it. This will cause the engine to idle rough.

Read also: 5 Important Tips for Parking a Manual Transmission Car

Things to Remember

Your engine should normally get to around 700 RPM after you start the vehicle. If it is a few hundred RPM under or over that amount and you experience one or more of the problems listed above, then you will want to diagnose the issue right away.

The cost of the repair or replacement job will depend on what the cause was. If you take your vehicle to a repair shop soon, then your engine should be okay.

But if you’ve continued to let it idle poorly for too long, then there could be irreversible damage to the engine. This in turn could cost you thousands of dollars in repair or replacement costs. So, don’t wait for this to happen.

2 thoughts on “5 Causes of a Rough Idle or High RPM in Your Car”

  1. I have an exhaust leak I’ve got a broken bolt in the exhaust manifold so I can’t get a bolt in it I now have a jeep wrangled that idles too high just started today I’ve not drove it very far how much will this cost if I take it to a jeep dealership to fix it


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