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
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
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 >
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 >
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 >
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 >