One of the most (surprisingly) common faults in petrol-powered cars is shaking when idling or accelerating. While there isn’t necessarily one thing that it will always be, the most common cause of your engine shaking is a misfire.
What is a misfire?
In a petrol car, the motor relies on a couple of key things to be able to run efficiently (or at all).
1. Spark
2. Air
3. Fuel
Without a doubt, these 3 things are drilled into every apprentice mechanic the first time they have to diagnose any kind of no-start or misfire situation and, a misfire can come from any of these things.
However, while a misfire can come from any of these things, the most common cause is always related to spark. Spark plugs, coil packs and ignition leads all play a drastic roll in transporting and firing a spark at exactly the right time.
Because of the constant exposure to the high heat of the engine bay and high voltage, it’s far more common than you would think for these parts to wear out and, spark plugs are even replaced as a part of servicing your car.
When your car begins to shake like this, it is often best to have a mechanic diagnose the issue directly instead of just replacing the spark plugs, leads and coils. This is because some of these parts are actually quite expensive and can have a really significant lifespan if in reasonable shape.
While a spark plug may only be only $10ea in parts, a new coil might be over $200 in parts, or the total cost of replacing the spark plugs.
Realistically though, 9/10 of any misfire or shaking diagnosis will only ever take 1 hour of time with a mechanic and will let you know exactly what needs replacing instead of just firing the parts cannon.