When a car sputters as it idles, this means the car is either not getting enough power or fuel. To test the problem, the driver presses down on the gas peddle. If doing so makes the car stop sputtering, there is a problem with fuel delivery. If this does not help, there is a problem with the power supply.
There are many reasons why a car is not getting adequate fuel delivery. The first thing to check is the fuel pump. When a fuel pump is malfunctioning, this causes a car to sputter while idling. It is also possible that there is a blockage in the fuel lines. Although it is a less common cause, bad or malfunctioning spark plugs also cause cars to sputter frequently while idling.
The most likely causes of a power deficiency are a clogged fuel filter or a bad catalytic converter. Fuel filter cleaner and premium gas help to see if the fuel filter is clogged. To test the catalytic converter, drivers should drill a hole in the center. If air flows through the hole, this part is functioning correctly. If there is no air flow, the catalytic converter needs to be replaced.
Other less common causes of a car idling roughly include a malfunctioning distributor cap, frayed ignition wires or the ignition timing needing to be adjusted.