Did you know why is your car running rough at idle? Rough idle, while the engine is running, indicates that there is engine misfiring on one or more cylinders. Since the cylinder is misfiring the engine becomes imbalanced and that imbalance creates a rough idle.
Now, the real problem here is why the engine misfire? several reasons why the engine misfires, lot of factors must be considered that is why it's very difficult to test the engine. But, there are only two common faults that usually causing the problem, first, there might be a vacuum leak and the second is a bad spark plug or spark plug wires.
There is another reason but commonly encountered on high mileage cars, that is a burned or out of adjustments valve. If this is the case the affected engine cylinder will encounter low compression thus misfiring occurs. However, for fuel injection cars it is possible that the fuel injector is clogged which resulted in the engine misfiring. Since one injector is clogged, there will be fuel starvation on the affected cylinder which will make the engine rough during idle.
Possible Cause of Engine Rough Idle
1) Vacuum leak2) Bad spark plug or wires
3) Burn out valves
4) Out of adjustment valves.
What to do?
The first is to replace the spark plug and the spark plug wires, most of the time this will solve the problem rough idle. Refer to your car service manual that covers the car model to know how to replace the spark plug or spark plug wires if the problem still occurs bring the car to a reputable repair shop let the mechanic inspect the car to confirm the cause of the rough idle car engine.
Vacuum Leak
In a normal condition engine, all of the air coming from the intake is directed through the throttle body. In the throttle body, a mass airflow sensor measures the quantity of air that goes into the engine. There is a vacuum leak if the air enters the intake manifold without passing through the throttle body, thereby causing the mass airflow not accurately measures the amount of air entering the engine and this will result in a lean air-fuel mixture. Usually, the reason for a vacuum leak is a problem with the intake hose, a crack, or breakage on the hose that connected the intake manifold.
Burn out valves
A burnout valve is an indication that the valve is not sealing correctly. Hot gasses will leak (escape) and pass to the edge of the valve, eventually the valve burn. Overheating is can cause this, another reason is the use of fuel not recommended by the car manufacturer.
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