Why is my Mercedes-Benz giving a rough idle and fuel smell — could it be a purge control valve issue?

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Why is my Mercedes-Benz giving a rough idle and fuel smell — could it be a purge control valve issue?

I drive a Mercedes C200 W204, and lately I’ve noticed a rough idle, occasional engine hesitation, and sometimes a strong petrol smell near the car, especially after refueling. A local mechanic in Karachi mentioned it might be the purge control valve EVAP system. How common is this issue in Mercedes-Benz cars in Pakistan, and can bad fuel o r local climate contribute to this problem?

Talha Kyanii asked on 11 Oct 2025 10:59:27 am

1 Answer

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Gari Master - on 11 Oct 2025 11:01:16 am

Yes, rough idling combined with a petrol smell, especially after refueling, is a classic sign of a faulty purge control valve part of the EVAP system. In Pakistani conditions, this issue is quite common, especially in used Japanese imports and older models like the W204.

Possible causes include:

Stuck-open purge valve – Allows fuel vapors to enter the intake at the wrong time, causing rough idle o r engine hesitation.

Clogged o r malfunctioning valve – Can lead to poor fuel-air mixture, especially in stop-and-go traffic common in Karachi, Lahore, and Islamabad.

Bad-quality fuel – In Pakistan, fuel quality is inconsistent, and additives o r impurities can cause the valve to gum up o r stick.

What to do:

Have the valve tested using a diagnostic scanner live EVAP data.

If the valve is stuck open o r closed, it should be replaced.

Always use high-quality fuel and periodically clean the EVAP system components in dusty o r humid cities.