Why does my car idle high?

Answer

There are many reasons a car idles fast, but one common reason is a vacuum leak. Older muscle cars have only two or three vacuum hoses, making finding the leak easy. Newer vehicles have complex vacuum systems to reduce emissions, so leaks are more difficult to find. Popular Mechanics suggests spraying carburetor cleaner on a suspected leak and listening for the engine speed to increase.

An overheating engine increases the speed at which a vehicle idles. The overheating condition often leads to more serious consequences, such as a blown head gasket or a warped head. About.com recommends preventing the potential damage and stopping the fast idle by repairing the cooling system.

Ignition timing affects the idle speed. A timing light quickly reveals problems with vehicle timing and allows the user to adjust it to the manufacturer's recommended specifications.

On vehicles with a powertrain control module, issues with the on-board computer may affect idle. Older vehicles experience similar problems due to problems with the distributor cap, rotor, plugs or wires. About.com suggests testing the control module with a scan tool and replacing defective ignition parts.

A failing alternator may also affect the engine idle. In this case, when the alternator is replaced the speed returns to normal.

A fuel pressure regulator operating incorrectly also increases the engine's idle speed. This is not a do-it-yourself job, so drivers should have a mechanic check the pressure using a fuel pressure gauge and replace if necessary.

Q&A Related to "Why does my car idle high?"
Automobiles use vacuums to adjust and control various engine components. A leak in a vacuum hose will cause a loss of vacuum power that might result in a high idle. Check vacuum hoses
http://www.ehow.com/facts_7657746_car-idle-high-pa...
A vacuume leak at the intake manifold or vacumme hose can cause a high idle. On carbuerated vehicles the idle adjustment screw may be set to high. On fuel injected vehicles, the Idle
http://wiki.answers.com/Q/Why_would_a_car_idle_too...
A vacuum leak at the intake manifold or vacuum hose does. On carbuerated vehicles,
http://www.chacha.com/question/what-causes-a-car-t...
Your fast Idle sensor maybe stuck open.When you start the car the fast Idle sensor is open to allow more air to the motor, Which causes a higher RPM . after it starts the fast Idle
http://answers.yahoo.com/question/index?qid=200803...
1 Additional Answer
Ask.com Answer for: why does my car idle high
Why Does My Car Idle High in Park?
A high idle when a vehicle is in park is not only annoying, but it is also a sign of a problem in the engine. Finding and repairing the problem likely will improve fuel efficiency and provide better engine performance.... More »
Difficulty: Easy
Source: www.ehow.com
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