Engine Misfire Symptoms: Causes, Risks and What to Do
Written by Petro Olekhnovych, mobile mechanic in Aylesham, Kent
The most common engine misfire symptoms are a shaking or juddering engine, a rough idle, hesitation or lost power when you accelerate, and an engine warning light that comes on or flashes. A misfire means one or more cylinders are not firing as they should. If the engine light is flashing, pull over when it is safe, switch off and get the car checked before driving on.
What is an engine misfire?
Each cylinder in your engine needs the right mix of air, fuel and a spark at the right moment. The AA describes a misfire as one or more cylinders not firing up as they should.
When that happens, the cylinder stops pulling its weight. The engine runs unevenly and you feel it through the car.
A misfire can be constant, or it can come and go. Some only show up when the engine is cold, under load or in wet weather.
Engine misfire symptoms to look out for
The AA and RAC list these common signs:
- Rough idle. The car shakes or shudders while stopped at lights.
- Sluggish acceleration. The car hesitates, stumbles or feels down on power when you press the pedal.
- Juddering. The RAC links misfires to a sudden juddering engine.
- Stalling. The engine cuts out unexpectedly.
- Engine warning light. It may stay on or flash.
- Unusual exhaust smoke, or popping and spluttering sounds.
You may also notice the car using more fuel than usual.
Warning light on? We come to you.
Send a photo of the dashboard and your reg. We will tell you if it looks safe to drive and what it needs.
WhatsApp for a free quote Call 07563 350335
Labour £30 to £50 per hour depending on the job. Send your reg number and we will reply with a price before any work starts.
Is it safe to drive with a misfire?
It depends on the warning light, and on how the car feels.
The AA says a flashing engine management light is more serious than a steady one, and can point to a problem such as a misfire. Its advice is to pull over as soon as it is safe, switch off the engine and call your breakdown provider.
The AA also warns that a flashing light could mean a problem affecting the catalytic converter. That is because unburnt fuel from the misfiring cylinder goes into the exhaust, which can damage it. Delaying the repair can make it much more expensive.
If the light is steady and the car drives normally, the AA says you can usually finish your journey. Get it checked soon. The RAC warns that a misfire left alone may lead to serious engine damage.
Our advice is simple. If the car is shaking badly, losing power or the light is flashing, stop driving it.
What causes an engine misfire?
A misfire usually comes down to a problem with spark, fuel, air or compression. The AA and RAC list these common causes:
- Spark plugs or ignition coils that are worn or faulty.
- Fuel injectors that are clogged or faulty, or a wrong fuel mixture.
- Sensor problems, such as the oxygen sensor. A failing camshaft or crankshaft sensor can make the engine time the spark wrongly.
- Air leaks, such as a vacuum leak or a manifold gasket leak.
- Mechanical wear, such as worn piston rings or a head gasket leak. These are usually the more expensive repairs.
Because so many parts can cause the same symptoms, guessing is costly. Replacing spark plugs will not help if the real fault is a leaking injector.
How a misfire is diagnosed
Modern cars store fault codes when the engine control unit detects a misfire. A code such as P0300 points to random or multiple cylinder misfires. Other codes can point to a specific cylinder.
A diagnostic check reads those codes. The code alone is a starting point, not the answer. A good mechanic then tests the likely parts on that cylinder to find the actual cause.
The AA advises a professional diagnosis using the right equipment, rather than guesswork. Fixing the root cause is what stops further damage.
If your car is also simply feeling slow without obvious shaking, read our guide on why a car loses power when accelerating.
What a misfire repair costs, and why it varies
We cannot give one price for a misfire, because the cause decides the job. A loose connection or a single worn part is very different from a head gasket problem.
The things that affect the cost are:
- What the cause turns out to be.
- Your car’s make, model and engine layout. Some engines make plugs and coils easy to reach, others do not.
- The price of parts for your car.
- Whether the misfire has already damaged anything else, such as the catalytic converter.
Acting early usually keeps the bill down. Regular servicing helps too, as worn parts get spotted before they fail. See our car service checklist for what a service should cover.
How we can help
We are a mobile mechanic, so we come to your home or workplace. We cover Aylesham, Canterbury, Dover, Deal, Sandwich, Folkestone and the villages in between. See all the areas we cover.
We can carry out fault finding on your car, read the codes and track down what is causing the misfire. Then we tell you what it needs before any work starts.
Labour is £30-£50 per hour, depending on the job and how difficult it is. Parts are extra. We agree the price with you on WhatsApp first, so there are no surprises.
You can also book an appointment here.
Frequently asked questions
Can a misfire fix itself?
Sometimes it seems to disappear, for example once the engine warms up. The cause is usually still there, so it is worth getting the codes read.
Can I drive to a garage with a misfire?
If the engine light is flashing or the car is shaking badly, the AA advises stopping as soon as it is safe. A mobile mechanic can come to you instead.
Will a misfire fail an MOT?
An engine warning light that shows a malfunction is a major defect in the MOT inspection manual, for both petrol and diesel cars. So yes, it can.
Does a misfire damage the engine?
It can. The RAC warns of serious engine damage if a misfire is ignored, and the AA warns of possible catalytic converter damage.
Need help? Send a WhatsApp to 07563 350335 with your car’s make and model and we’ll come to you.
Warning light on? We come to you.
Message us on WhatsApp with your reg and postcode for a price before any work starts.
WhatsApp for a free quote Call 07563 350335
Labour £30 to £50 per hour depending on the job. Send your reg number and we will reply with a price before any work starts.
