What Causes a Car to Sputter and Idle Rough

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What Causes a Car to Sputter and Idle Rough

What causes a car to sputter and idle rough? Car's engine that sputters and runs rough while idling is an indication of misfiring of one or more cylinders if the cylinders misfire the vehicle's engine balance will be disrupted.

There are several possible reasons that cause the engine to sputter and run rough hat may result in engine misfiring but the most common are:

What causes a car to sputter and idle rough

1) Bad valve
2) Bad coil or spark plug wires
3) If the car is equipped with fuel injector another possibility is that one or more injectors are clogged, which resulted in fuel starvation and creates misfiring.



Car Troubleshooting


If the engine also sputters when the engine is idling but not while driving, then the problem is a bad valve. When the car sputters both when starting and at idle. But, when you start driving, the sputtering goes away. it smoothes out. This is a telltale sign that the valves in the engine are not functioning properly.

Bad valve

What to do?
You need a valve job. Unfortunately, this is usually an expensive procedure. If this vehicle is not under warranty, you'll have to shop around for the best price. Make sure you only have the job done at a shop that specializes in this type of work.

If the engine sputters at most speed. Pull off one of the spark plug wires and carefully lay it close to the ground (any clean, grease-free, the metal surface will work). Have a friend crank the engine for a second by turning the ignition key.

As the engine is cranking, look for a spark that should jump from the end of the spark plug wire to the ground. Do this same procedure for all of the spark plug wires but make sure you put the last wire you tested back onto the spark plug before you go to the next one.

If the spark jump to the ground for all the spark plug wires tested, then there is a problem with the fuel injection system. The problem could be that your fuel injection system is not operating normally.

What to do?
Fuel injection systems are complex and hard to diagnose. If this vehicle is not under warranty, take it to a mechanic that has expertise in this particular make/model. We highly recommend you get a second opinion if the first mechanic suggests that you need a new fuel injection system. Very often, the problem is not the fuel injection system itself but rather one of its sensors. A skilled mechanic will be able to determine if all the sensors are working properly.

Clogged Fuel Injector

If the spark does not jump to ground for all the spark plug wires tested, then the problem is a bad coil or bad spark plug wires.

Bad Coil or Bad Sparkplug Wires

In the beginning, it was indicated that this car sputters while starting. However, the car also sputters at most driving speeds. This strongly suggests that there isn't ample current reaching one or more spark plugs, thus causing the engine to misfire or sputter. As you to check each of the spark plug wires. If at least one of the sparkplugs, you didn't notice a spark jump to the ground as the engine was cranking. This means that either the spark plug wire is bad or the coil isn't providing enough current to the spark plug wire.

What to do?
In this situation, it is hard for anyone but a professional mechanic to determine which is bad: the coil or the spark plug wires. If this vehicle isn't under warranty you'll need to find a mechanic. When talking to a mechanic, explain to him just what this article explained to you.

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