If your GTI's stumbling — a shake, a flashing light under load — I'll call it a coil pack before you've finished telling me. It's the most common misfire I see on any turbo GTI, the Mk4 1.8T and every EA888 since. Each cylinder's got its own coil, and they cook themselves with heat and age.
You'll usually get a cylinder-specific code — P0301 to P0304 — and that tells me exactly which one's dropped
…