When the engine is running it does sound like it would normally, it can sound like it's struggling to keep running or produce strange noises that sound like it's not running in time with itself.
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.
There are patches of fuel underneath the car or on parts of the underside of the car, the liquid smells like petrol.
When putting your foot on the accelerator the car does not respond with the same urgency of acceleration. It feels like there is a lag between putting your foot down and the car accelerating, when it does accelerate it feels like a much slower change in speed.