Why do some Mercedes engines in Pakistan experience rough idling o r engine misfire, especially in older models?

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Why do some Mercedes engines in Pakistan experience rough idling o r engine misfire, especially in older models?

Many Mercedes owners in Pakistan especially with models like the C200 o r E-Class from early 2000s to 2015 report that their engines run unevenly o r vibrate while idling. Mechanics often suggest things like bad spark plugs, coil packs, o r even fuel injectors. Could this be linked to Pakistan’s fuel quality, lack of regular tuning, o r is it a common Mercedes-specific issue? What’s the best way to diagnose this locally?

Talha Kyanii asked on 20 Sep 2025 17:18:34 pm

1 Answer

28 views |

Gari Master - on 20 Sep 2025 17:21:25 pm

Most common causes in Pakistan:

Bad spark plugs o r ignition coils — These wear out over time, especially in dusty o r humid conditions. Misfiring and rough idle are often caused by coil failure especially on older M271 o r M274 engines.

Poor fuel quality — Pakistani fuel sometimes has impurities o r lower octane than what Mercedes engines are tuned for, causing incomplete combustion.

Dirty o r failing fuel injectors — Clogged injectors from long intervals between cleanings o r low-quality fuel can lead to misfires and uneven idling.

Carbon buildup — In direct injection engines common in newer models, carbon deposits on intake valves can cause poor combustion and vibration at idle.

What to do:

Scan for fault codes OBD2 to isolate which cylinder is misfiring.

Replace all spark plugs and inspect coils especially after 40,000–60,000 km.

Use high-quality fuel preferably 92+ RON and fuel system cleaner every 5,000–10,000 km.

Consider an intake valve cleaning if misfire persists in direct-injection models.