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.


Is this answer helpful?

Similar Questions

  • Q:

    What rpm should my car idle at?

    A:

    Idle speeds vary from car to car, but for a passenger car, typical idle speeds are between 500 and 900 rpm. This idle speed also depends on the accessories that are currently running as a car's idle control system will automatically raise the idle in order to provide power for auxiliaries such as air conditioning and power steering.

    Full Answer >
  • Q:

    What is happening when a car vibrates at idle?

    A:

    A car or car's engine may vibrate while idling for various reasons, including that the motor or transmission mounts have a problem. When a car is stopped at a red light or turned on in park, a noticeable vibration may occur that signals damaged or broken transmission mounts.

    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:

    Why does my car idle high in park?

    A:

    Possible causes of a car idling high while in park include the car having a bad accelerator, an overheating engine, the fuel pressure regulator operating at low pressure and the alternator acting up. One symptom of the car's idling problem is the driver having to apply brakes intensely when parked.

    Full Answer >

Explore