Toyota iQ engine power loss and jerking

Sounds like detonation, possibly pre-ignition. Are you using the correct octane fuel? Deposits in the combustion chamber can cause hotspots, leading to premature ignition. That's what 'knocking combustion' means. Has the engine been tuned recently, or have the cylinder heads been worked on?

I always use the recommended fuel, and the engine hasn't been tuned. Cylinder heads are untouched. Could deposits really cause all these symptoms? How critical is this issue?

Yes, carbon deposits are a likely culprit given the symptoms and mileage. They increase the compression ratio and create hot spots. Detonation, if left unchecked, can cause serious engine damage. I'd suggest a workshop visit for a diagnostic and potential combustion chamber cleaning. It could save you bigger problems.

Thanks for the info! The workshop confirmed carbon deposits. They cleaned the combustion chamber, and it's running much better. Cost me 425€, but worth it to avoid further damage.