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Alvin Knex
Rough Idle in Cold Weather
Asked: 1 year, 2 months ago • Category: Frequently Asked Questions

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?

Answers

Accepted Answer

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.

Jimna Mustafa
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Replies (3)

Alvin Knex : If it’s the O2 sensor, why would it only happen when the engine is cold? Wouldn’t it affect performance all the time?

Jimna Mustafa : Good observation! Many O2 sensors only become active once the engine reaches operating temperature. When cold, the engine runs in 'open, loop' mode and ignores the O2 sensor, relying on preset fuel maps. If the sensor is failing, it might only cause issues once it starts influencing the fuel mixture, or if it sends incorrect signals during warm-up.

Alvin Knex : Turns out the upstream O2 sensor was failing. Swapped it out, and the violent shaking is gone. Thanks for pointing me in the right direction!

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