My 2018 Honda Civic shakes violently when idling on cold mornings. RPMs fluctuate between 500 - 1000. No check engine light. Changed spark plugs last month but issue persists. Could it be a vacuum leak or bad oxygen sensor?
Yes, a faulty O2 sensor can cause this issue. It helps regulate the air-fuel mixture. If it's not working properly in cold conditions, the engine may run too rich or lean, resulting in rough idling and vibrations.