Seat Leon engine misfire diagnosis

Rough running and misfires, eh? Sounds familiar. Had a similar issue with my old Volvo, although that was a diesel. Check engine light was on, and it felt like driving a tractor. Have you checked the ignition coils? They can cause similar symptoms and are easier to test than the fuel injectors. If those are fine, then injectors are the next suspect. It could also be a vacuum leak, but that usually affects more than one cylinder. Think of it like a clogged artery in your engine's fuel system.

Thanks for the quick reply. Ignition coils seem okay, I tested them with a multimeter. But how can I be absolutely sure it's the fuel injector? Is there a definitive test I can perform myself before taking it to the workshop?

If you've already checked the ignition coils and they seem fine, and you're still getting misfires, especially if it's isolated to a specific cylinder, then it's highly likely to be the fuel injector. A mechanic can perform a fuel injector test, checking the spray pattern and flow rate. You could try using injector cleaner, but it's often a temporary fix. In my case, with the Volvo, it turned out to be a completely dead injector. Eventually, you will need special equipment to properly diagnose the issue, so I suggest taking it to a workshop.

Took the Leon to a workshop. They confirmed a faulty fuel injector. Replaced all four, costing 515€. Engine runs smoothly now, throttle response is back, and the check engine light is off. Thanks for the advice.