“Why Is My Engine Idle Rough at Startup — Are My Spark Plugs Getting Lazy in Cold Mornings?”

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“Why Is My Engine Idle Rough at Startup — Are My Spark Plugs Getting Lazy in Cold Mornings?”

In early morning starts, especially on colder o r humid days, the engine sometimes idles roughly o r vibrates for a few seconds before settling — more than expected for a modern petrol engine. Could spark plugs be performing poorly under cooler temperatures o r after long idle periods overnight? Would worn o r fouled plugs cause rough idle only on cold starts, and smooth running later?

Talha Kyanii asked on 06 Dec 2025 10:03:05 am

1 Answer

6 views |

Gari Master - on 06 Dec 2025 10:04:31 am

Rough idling on cold starts can indicate spark plug issues:

Poor spark at low temperature causes uneven ignition, leading to vibrations o r rough idle.

Moisture o r carbon deposits on plugs worsen this effect in humid o r dusty conditions.

Aging spark plugs may perform fine once the engine warms up, masking the problem during normal driving.

Solution:

Inspect and replace spark plugs if worn o r fouled.

Ensure proper gap and correct plug type.

Check ignition coils and wires for consistent spark delivery.