Seat Altea rough running at idle

Rough running and stalling? Sounds painfully familiar. I had a similar issue with my old Renault Megane – though it was diesel. Was the coil pack itself visibly damaged? Have you checked for obvious cracks or burning? What about the wiring harness and connector? Are they secure and free from corrosion? Just thinking out loud here. The symptoms you describe could also point to a dodgy sensor, but with the check engine light on, you should have some error codes to narrow it down. Did you read them out?

The coil pack itself looks fine externally. No visible damage, cracks, or anything obvious. I did check the connector; it seemed secure, but I didn't specifically look for corrosion. Where exactly should I be focusing my attention regarding the wiring harness? Any specific points that are prone to failure? I'm assuming you checked the error codes on your Renault?

Yep, I checked the error codes. It pointed directly to a cylinder misfire, which, in my case, was also the ignition coil. As for the wiring harness, check where it bends or is secured to the engine. Vibration and heat can cause the wires to fray or the insulation to crack. Given that you've checked the obvious stuff, it's probably time to get it properly diagnosed. A workshop can do a proper test of the ignition system. Better than blindly replacing parts, right?

Just wanted to close the loop. The workshop confirmed it was a defective ignition coil. They replaced it, including labor, for 95€. Runs like new again. Thanks for your input; it definitely helped confirm my suspicions.