You are sitting in your car at a traffic light, the engine is running, and you feel vibrations coming through the steering wheel, the gear lever, or the whole car. Sometimes it is a barely noticeable tremor, other times it is a proper shake. Either way, something is not right. Here are the most common causes we see in the workshop.
Worn Engine Mounts
Engine mounts (hydraulic or rubber) are designed to absorb engine vibrations and prevent them from transferring to the body. When they wear out, every vibration from the engine passes straight through to the chassis.
How to recognise it: Vibrations are most noticeable at idle with the air conditioning on or when you shift into D on an automatic. If you watch the engine while someone revs it, you will see it moving around more than it should.
Replacing engine mounts is not complicated, but it is important to replace the right one. Usually the lower or front mount fails first because it carries the most load.
Spark Plugs and Ignition Coils
On petrol engines, worn spark plugs or weak ignition coils cause one or more cylinders to misfire. When a cylinder is not firing properly, the engine vibrates because it is unbalanced.
How to recognise it: The vibrations come with a slight jerk, and sometimes a check engine light. Diagnostics usually show a misfire code on a specific cylinder.
Spark plugs are cheap and quick to replace. Coils are a bit pricier, but still a straightforward job. This is one of those repairs you feel immediately. The difference is like night and day.
Irregular Idle (Idle Control)
At idle, the engine should run at stable RPMs, usually around 800. If the RPMs jump up and down or drop too low, the car will shake.
Most common culprits: A dirty throttle body, a faulty IAC valve (idle air control), or dirty sensors. On newer engines, a throttle body adaptation via diagnostics often resolves the issue without replacing any parts.
Vacuum Leak
The intake manifold and vacuum hoses must be airtight. Any leak allows excess air into the engine, throws off the mixture, and causes rough running.
How to recognise it: The engine shakes at idle but settles down when you give it a little gas. Sometimes you can hear a slight hissing from the engine bay. A vacuum leak can be found with a smoke test or by carefully inspecting all the hoses and connections.
EGR Valve
A clogged or stuck-open EGR valve lets exhaust gases into the intake manifold while the engine is at idle. This disrupts engine operation and causes vibrations.
On diesel engines, this is an especially common cause of idle shaking. Cleaning or replacing the EGR valve solves the problem. On certain models (Golf 5, Passat B6), this is such a frequent issue that we check it first.
Fuel Injectors
A faulty injector does not deliver fuel evenly, so the cylinder does not fire correctly. On diesel engines, injectors that dribble instead of properly atomising fuel cause rough idle.
How to recognise it: On a diesel, you will also notice an unusual knocking sound that is different from the normal diesel clatter. Diagnostics with a fuel return measurement on the injectors gives a clear answer.
What to Check First
If your car shakes at idle, start with a diagnostic scan. A fault code reader often points to the exact cylinder or system causing the problem. If you do not have a scanner, pay attention to whether the vibrations change when you turn on the air conditioning, shift into gear, or give it a little gas. That helps narrow down the cause.
These are faults that do not usually get worse overnight, but they do not fix themselves either. If you notice a shake that was not there before, get in touch so we can take a look. Most of the time it turns out to be a simple and inexpensive repair.