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.
At idle speed the engine sounds like it's about to stall, it improves when the accelerator is pressed down but when idling in traffic it sounds like it's struggling to run properly.
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.
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.