A rough or unstable idle in your vehicle
Is your idle rough? Does the RPM have a tendency of going up and down? There are several factors that may be at the heart of the problem, and generally it is not terribly expensive to solve. Often, the most difficult part is to determine exactly what is causing the issue.
What are the possible causes?
In gas engines, ignition problems (poorly synchronized sparks produced by the spark plugs) can cause a rough idle. The ignition distributor may also be responsible as it is a part of the ignition system.
A seized fuel injector in a gas or diesel engine will cause the idle to feel rough since the cylinder powered by it will be defective. Also be sure to check the wiring of your injectors to make sure they are not oxidized. Oxidation of these components can also cause a rough idle.
The fuel pressure regulator (located toward the injection pump) is often the cause of idle issues.
Sometimes the throttle body can malfunction or become clogged, therefore preventing the butterfly valves from putting themselves correctly into place. When you accelerate, the butterfly valves open, and close when you release the accelerator. If the issue is not persistent and only occurs in cold weather, then there’s no need to be concerned. This problem is more commonly a concern for gas engines, as unlike gas engines diesel engines don’t need a throttle body (although one was added on modern blocks for technical reasons).
Yes, there exists a component who is responsible to regulate the vehicle’s idle. It is also called an idle air control actuator or idle air control valve, and is located toward the throttle body. It is possible for this part to become dirty and therefore malfunction.
The purpose of the lambda probe is to measure the proportion of oxygen in the gas or liquid being analyzed by the engine control unit, to make sure that the engine burns its fuel efficiently and cleanly. If the lambda probe malfunctions, it can result in an abnormally slow idle.