Rough idles are among the most frustrating problems that you can experience in a car. In some cases, it might be a subtle problem that's barely noticeable to anyone who isn't already familiar with how the car should behave. In other cases, a rough idle might be severe enough that there's no mistaking that something is seriously wrong. Often, a car that is idling poorly will feel as though it is about to stall, and the engine may have difficulty finding a steady idle speed.
Whatever the case, diagnosing these problems can be tricky, especially if the car's computer is not throwing any obvious trouble codes. There is an almost endless number of potential causes for a rough idle, but these are a few of the most common.
Vacuum leaks are perhaps the number one most common cause of poor idling conditions in modern vehicles. Your motor's vacuum is produced by the differential in air pressure between the atmosphere and the intake manifold. This differential is a fundamental and necessary part of the motor's operation, but it is also used as a method of creating mechanical work that is used by a number of other important components in your vehicle.
Because so many components make use of it, your engine bay is likely stuffed with various vacuum lines. Engine efficiency and power decrease greatly if the motor is unable to produce enough vacuum, and this situation can occur if one of those many lines has an air leak. Vacuum leaks such as this can sometimes trigger a variety of seemingly unrelated trouble codes, or they can simply produce an engine that feels rough and down on power. Whatever the case, proper diagnosis of a vacuum leak generally requires a smoke tester and should be performed by professionals.
Nearly as common as vacuum leaks are issues with a vehicle's ignition system. For typical combustion engines, the mixture of air and fuel in the combustion chamber is ignited by an electrical arc created by the spark plugs. Smooth, consistent spark is necessary for your engine to operate, and any sort of interruption in the ignition system can easily cause your car to idle poorly or even stall. Spark plugs are typically long-lived components, but they can cause misfires and other drivability issues when they fail. Likewise, spark plug wires will typically need to be replaced on higher mileage vehicles as well.
Note that many vehicles use a coil-on-plug system. If this is the case for your car, then you won't have separate spark plug wires that will need to be replaced. Unfortunately, failing ignition coils can cause similar symptoms, and they must also be considered possible culprits if an ignition system problem is suspected.
Bad O2 Sensors
Did you ignore a check engine light because it just pointed to a sensor? Unfortunately, a malfunctioning O2 sensor can begin to cause noticeable drivability issues as it fails completely. As part of its job as an emissions control device, your O2 sensor helps your car's computer determine the proper mixture of air and fuel to use. Without proper input, your engine can potentially run lean or rich, resulting in reduced gas mileage, poor performance, and a rough idle.
Of course, these are far from the only possible causes of a rough idle. If your car is running poorly, your best bet is to have it diagnosed by a professional technician who can help you to pinpoint the issue and get your car running smoothly again. To learn more, check out a website like http://www.autorepairhighdesert.com/.