Q:

Why does a car idle rough?

A:

Quick Answer

There are a variety of problems that can cause a car's idle to be rough. A rough idle is usually defined by the car idling below its normal speed, loping RPMs, a skipping sound or in a way that causes the car to shake. Idle problems can often be a clue to something more serious going on, so it is best for car owners to get them checked out.

Know More
Why does a car idle rough?
Credit: Image Source Image Source Getty Images

Full Answer

The simplest reason for a rough idle is either a vacuum leak or an incorrect idle speed. A vacuum leak causes air to get into the system and disrupt the normal idling speed. Idle speed is a setting on most cars, and some cars require only a simple tool like a butter knife to correct this. However, the idle speed should not change randomly and another problem is likely to be lurking beneath the surface.

Dirty fuel injectors are another possibility for a rough idle. Fuel injectors do need to be periodically cleaned throughout their lifetime as fuel deposits build up and eventually interfere with the car getting proper fuel. Lack of fuel is similar to lack of air and the idle speed is affected. Other possibilities include spark plugs or the distributor cap and wires.

Learn more about Car Parts & Maintenance

Related Questions

  • Q:

    Why does a car misfire when in idle?

    A:

    There are a number of reasons why an engine might misfire while it is idling. Usually misfires occur when there is no spark, the air/fuel mixture is out of balance or the engine is losing compression.

    Full Answer >
  • Q:

    Why does my car idle at a high rpm?

    A:

    A car that is cold has a fast idle to quickly bring it to optimal operating conditions. This is a part of the design of the engine. Older vehicles with carbureted engines have a choke to increase the idle speed to as high as 1200 rpm, or revolutions per minute, until the engine warms, according to About.com.

    Full Answer >
  • Q:

    What causes a car to run rough?

    A:

    Reasons for a car running rough can include problems with the engine temperature or oxygen sensors, bad hoses, ignition system or timing problems, clogged air or fuel filters, and faulty spark plugs or fuel injectors. Many problems that manifest through a rough idle can be easily fixed.

    Full Answer >
  • Q:

    Why does my car idle rough at a stop?

    A:

    Cars idling rough at stops can have many causes, including damaged sparkplugs, improperly installed sparkplugs or damage to the car's fuel injector, carburetor, vacuum hoses or ignition wires. It is important to take a car to a certified mechanic soon after it begins idling roughly in order to prevent more expensive damage.

    Full Answer >

Explore