Common Car Misfire Symptoms and How to Diagnose Them

Car misfire symptoms

(1) The engine sputters and idles rough.
(2) Car shakes at idle.
(3) The engine lacks power.
(4) Engine stalls while accelerating.

Car troubleshooting

An engine that runs rough while idling indicates that one or more of its cylinders is misfiring. This is simply because misfiring cylinders disrupt an engine's natural balance. Now, you are probably wondering what specifically causes a cylinder to misfire? Well, there are many, many possibilities but unfortunately, none are very easy to test for. This is why the above (very general) diagnosis was suggested. Incidentally, two common causes of cylinder misfire are 1) a vacuum leak, and 2) bad spark plugs or spark plug wires. Additionally, since this vehicle is equipped with fuel injection (as was indicated in its profile), it is possible that one or more fuel injectors could be clogged. This will create a "fuel-starved" condition in the corresponding cylinders and thus misfiring.

What to do?

You might try replacing the spark plugs and spark plug wires. This is a procedure you can do yourself and it may solve this rough idle problem. However, if it doesn't or you don't feel too comfortable doing this, you will need to take this vehicle to a garage for complete analysis and repair. Please try to find an AAA approved garage. Such garages tend to be reputable and, best of all, if you have a dispute after any work is done, the AAA has the policy to investigate and resolve the situation.

As indicated, this engine runs roughly, especially when idling. This basically means the engine is misfiring. Such a condition causes a lack of power simply because the engine isn't operating efficiently. Misfiring is either caused by a fault in the ignition system or, a "hard" engine problem (for example, a stuck valve). For the car with low mileage, we are guessing the cause is probably ignition-related. In particular, one or more spark plugs or spark plug wires are probably bad. Clearly then, if the spark isn't occurring in the combustion chamber when it's supposed to (due to a bad plug/wire), the engine will not only run rough, it'll also lack power.

What to do?

For a particular car with very low mileage. It is most likely under warranty. Hence, go to your dealer for analysis and repair. If the mechanic does determine that one or more of the spark plugs or wires are indeed bad, be prepared to pay for their replacement since warranties generally don't cover such items.

Each of the car engine's cylinders must fire properly and in the correct order for the engine to run smoothly. If one or more of the cylinders isn't firing as it should, the engine's balance is thrown off. This causes the engine to shake especially at idle and thus, the entire vehicle to shake as well. The most common causes of misfiring are bad spark plugs, bad spark plug wires and, a faulty distributor cap. Any of these will adversely affect the firing of the air/fuel mixture in the engine's cylinders.

What to do?

Start by replacing the spark plugs and spark plug wires and hold off for now on the distributor cap. New plugs and wires may be all that's necessary to cure the misfiring. But, if this doesn't correct the problem, then go ahead and replace the distributor cap. By the way, any auto parts store will carry the spark plugs, wires, and distributor cap for this vehicle.

The procedure to replace these items is simple and can be found in any repair manual covering this vehicle. If you don't want to do the work yourself, you'll need what most garages call a "maintenance tune-up". This will cover the three items mentioned above. Incidentally, if this vehicle is still under warranty, the above-mentioned items won't be covered.

Engine stalls while accelerating and car hesitate and even jerks on cold mornings. As indicated, this acceleration problem typically occurs on cold, wet mornings and, when the engine is cold. What is probably going on in this situation is the following. During the night, condensation (i.e. moisture) forms on the inside of the distributor cap. This is due to the cold and wet weather and the fact that the engine is cold. This moisture allows electrical current to arc inside the distributor cap and, this arcing consequently causes the engine to misfire. When misfiring occurs, the vehicle will hesitate simply because the power or "pull" the engine is producing is not even.

What to do?

The next time you expect rain or any other wet weather, park this vehicle inside the garage for the night. This should help prevent moisture from forming inside the distributor cap.