Seat Altea cold start issue

Rough idle on cold starts for your Altea could definitely point to a fuel delivery issue. Have you tried any injector cleaning solutions? An injector test could also reveal if one's not performing as it should. It's like a clogged artery in your car's fuel system!

Injector test, interesting. Is that something I can do myself, or does it require specialized equipment? And would injector cleaning really make a difference given the mileage?

The injector test needs proper gear, so a workshop is your best bet. While injector cleaning might help in some cases, with those symptoms, it's more likely a defective injection valve. Imagine trying to unclog a drainpipe that's actually cracked – you'll only get so far.

Huge thanks for the insights. Turns out, the injector was indeed the culprit. 515€ later, it's running like a champ again!