Why Does My Car Feel Sluggish?
Ellie Dyer-Brown, 14 days ago
3 min read
- Diagnostic
FixMyCar discusses what can make a car feel sluggish and how to fix it.
It's frustrating when your car feels less responsive than usual - after all, nobody knows how it drives better than you. You'll notice even if there's only a small drop in performance.
This guide discusses what makes a car sluggish and what you can do about it.
Contents
1. Old spark plugs
Spark plugs provide the spark needed in petrol engines to start the combustion process. They typically last 30,000 miles or more before they need replacing.
Signs of worn spark plugs
Common symptoms of spark plug failure include:
How to fix it
Replacing the spark plugs is relatively easy with the right tools and knowledge. You can do it at home using the instructions in this guide.
If you prefer to leave the job to a professional, you could find a mechanic to handle it for you. According to our data, the average price of a spark plug replacement is £151.14.
2. Dirty air filter
Car engines rely on internal combustion, which requires the correct ratio of fuel and air. Since air is drawn in from outside, the air filter protects the engine by stopping contaminants from entering it. However, when the filter becomes blocked, it can seriously reduce your car's performance. It should be replaced every 30,000 miles or so.
Signs of a dirty air filter
Reduced fuel efficiency
How to fix it
Fixing this problem is simple - you need to replace the air filter, which is often done during a full service.
3. Faulty mass air flow sensor
The mass air flow (MAF) sensor measures the air entering the engine and sends this information to the engine control unit (ECU), which adjusts the air-fuel ratio accordingly.
When the sensor fails due to contamination or normal wear and tear, it results in an incorrect ratio of air and fuel, leading to a drop in performance.
Signs of a faulty MAF sensor
Hesitation and sluggishness
How to fix it
Book an appointment to have the sensor replaced. According to our data, the average price for a sensor repair is £95.09.
4. Faulty oxygen sensor
The oxygen sensor is also known as the lambda sensor. It's a small probe that sits in the exhaust system and helps to maintain the correct air-fuel ratio. Find out more about how it works in this guide.
Signs of a faulty oxygen sensor
Rough idling
Poor fuel efficiency
How to fix it
Book an oxygen sensor replacement, which costs £188.80 on average.
5. Clogged catalytic converter
The catalytic converter reduces emissions by changing toxic exhaust gases into less harmful substances like water vapour. This guide explains how it works.
Catalytic converters become clogged due to contamination from unburnt fuel, leaking coolant or oil. Unfortunately, if you discover your cat is blocked, an underlying issue probably needs fixing, too.
Signs of a clogged catalytic converter
Extreme heat from under the vehicle
How to fix it
Unfortunately, replacing a catalytic converter can be expensive. The average price is £433.80, according to our data. However, it's something you shouldn't put off because all cars must have a functional cat by law.
6. Faulty throttle position sensor
The throttle position sensor (TPS) measures how open the throttle valve is and sends this information to the ECU. The more open the valve is, the more fuel enters the combustion chamber.
Signs of a faulty throttle position sensor
Sudden surges in speed
Poor fuel economy
How to fix it
When the TPS fails, you'll have to replace it. On average, this costs £149.87.
7. Malfunctioning fuel system
A problem in the fuel injection system can result in the engine not getting enough fuel, leading to hesitation and sluggishness. Several parts could be to blame:
Clogged fuel filter
Dirty injector
Broken fuel pump
How to fix it
It's hard to know which part of the fuel injection system needs repairing without investigating under the bonnet, so the best thing to do is take your car to a mechanic. The average price of a fuel injection system repair is £210.04.
My car feels sluggish when accelerating
If your car feels slow when you press the accelerator peddle, there's likely an issue with the fuel system. However, the other faults identified in this guide could be to blame. Unless you're mechanically minded, you'll probably need the help of an expert to find out what's going wrong.
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