Jerking while driving is one of those symptoms that can mean ten different things. Sometimes it is a minor issue, sometimes it is serious. Here is how to tell what you are dealing with.
Fuel System - The Most Common Culprit
If the car jerks during acceleration, we look at the injectors and fuel delivery first.
Clogged injectors do not spray fuel the way they should, so the engine gets an uneven mixture. You feel it as a slight jerk, especially at lower RPMs. Cleaning the injectors at our workshop is a relatively straightforward job and often solves the problem completely.
A weakening fuel pump cannot maintain the required pressure, so the engine starves under load. A typical sign is jerking at higher speeds or going uphill.
A clogged fuel filter produces the same effect. If it has never been replaced and the car has over 100,000 km, start there.
Ignition - Spark Plugs and Coils
Worn spark plugs or weak ignition coils cause misfires. The engine skips one or more cylinders and you feel a jerk. On a four-cylinder engine, if one spark plug is not performing, the jerking is quite noticeable.
How to recognise it: The jerking is strongest when accelerating from low RPMs. At idle, the engine may vibrate slightly. If you have a check engine light along with the jerking, it is almost certainly an ignition problem.
From our experience, replacing spark plugs and inspecting the coils fixes the jerking in at least a third of cases. A relatively cheap repair that makes a big difference.
Gearbox and Clutch
With a manual gearbox, a worn clutch can cause jerking when pulling away or shifting gears. It feels like the car slips and then grabs suddenly.
With an automatic gearbox, jerking during gear changes can mean the transmission fluid is old or internal components are worn. If the car jerks when shifting from one gear to the next, do not ignore it.
Jerking in LPG Vehicles
We see this a lot since we work extensively with LPG installations. If the car only jerks on gas but runs fine on petrol, the most common causes are:
- LPG filters that are clogged and need replacing
- LPG injectors that are dirty or faulty
- Poorly calibrated gas maps that need adjustment
- MAP sensor that is not reading correctly
This is mostly a matter of regular LPG system maintenance. The gas filter should be changed every 15,000-20,000 kilometres, and calibration should be checked once a year.
When It Is Dangerous to Drive
Do not ignore jerking if:
- It appears suddenly and forcefully, especially at higher speeds
- It comes with power loss or engine stalling
- You feel jerking when braking, because that could be a brake issue
- The car jerks and pulls to one side at the same time
Mild jerking during acceleration is usually not urgent, but it should not be ignored because it gets worse over time.
What to Check First
If your car jerks, the simplest approach is to start with the basics: spark plugs, fuel filter, LPG filter if you run on gas. These items are relatively inexpensive and often solve the problem. If that does not help, a diagnostic scan will reveal the exact cause. Stop by and we will quickly figure out what is going on.