The engine doesn't start up very easily and will often not start at all. When it is running it can cut out completely without warning.
The dashboard warning light showing on this page (or one very similar, sometimes a slightly different shape or colour) has appeared on the dashboard and doesn't go off when the car is running.
When driving the car feels like it's vibrating, the sensation can be felt through the steering wheel but may also just be a general vibration noise inside the car.
The fuel gauge seems to be going down quicker than usual, the car is using more fuel when driving in the same way as before.
The engine sounds like it's not running correctly, the engine sounds rough as if it's not running in time.