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.
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.
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.