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Diagnosing and Resolving Engine Vibration Idle in Mercedes-Benz C Class W204 with M272 engine
The Mercedes-Benz C Class W204, equipped with the M272 engine, is praised for its balance of performance and reliability. However, one issue that owners frequently encounter is engine vibration at idle. This condition occurs when the engine shakes noticeably while idling sometimes accompanied by misfires and a check engine light.
Engine vibration idle not only reduces driving comfort but also signals underlying mechanical or electrical faults. Left unchecked, it can lead to costly repairs. In this case study, we’ll examine a real-world example of diagnosing and resolving engine vibration idle in a Mercedes-Benz C Class W204.
Vehicle Details
- Model: Mercedes-Benz C Class W204
- Engine: M272 V6
- Customer Complaint: Engine vibration at idle, check engine light, occasional misfire at stops
Customer Complaint
The vehicle arrived at the workshop with the following issues:
- – Check engine light illuminated
- – Noticeable engine vibration when idling
- – Rough idle and reduced performance
- – Misfires, especially during stops at traffic lights or when in neutral
These symptoms pointed to possible ignition or fuel delivery issues, requiring systematic diagnostics.
Diagnostic Process
Step 1: Short Test
A short test was conducted using Mercedes-Benz diagnostic equipment.
- – Finding: Misfires were logged across multiple cylinders.
- – Interpretation: This indicated ignition or combustion-related faults rather than a single-cylinder failure.
Step 2: ECU–Injector Communication
The connection between the engine control unit (ECU) and fuel injectors was tested.
- – Signals were transmitted correctly.
- – Wiring and connectors showed no damage.
- – Conclusion: The ECU was functioning properly, and injectors were receiving correct commands.
Step 3: Spark Plug Inspection
All spark plugs were removed and measured.
- – Finding: Several spark plugs had incorrect gaps, outside manufacturer specifications.
- – Effect: Incorrect spark plug gap leads to weak or inconsistent sparks, causing incomplete combustion and misfires.
Step 4: Injector Resistance Test
Each injector was tested for resistance values.
- – All injectors were within the specified range.
- – Conclusion: Fuel injectors were not the source of the vibration.
Step 5: Ignition Coil Inspection
The ignition coils were tested individually.
- – Two ignition coils were found defective.
- – Effect: Faulty coils fail to deliver voltage to spark plugs, leading to repeated misfires and rough idle.
Resolution
The following steps were carried out to resolve the engine vibration issue:
1. Spark Plug Replacement
- – Old spark plugs were replaced with new OEM parts.
- – Each spark plug was correctly gapped to manufacturer specifications.
2. Ignition Coil Replacement
- – Two defective ignition coils were replaced with new OEM coils.
- – This restored proper spark delivery to the affected cylinders.
3. Final Checks and Test Drive
- – Fault codes were cleared.
- – A test drive confirmed smooth operation with no vibrations at idle.
- – The check engine light remained off.
Result: The engine vibration idle problem was completely resolved.
Explore More Mercedes Engine Misfire Issues
For a deeper dive into all misfire-related problems, visit our hub page: Mercedes Engine Misfire Issues – Causes and Fixes. You’ll find grouped case studies, step-by-step diagnostics, symptom–cause–fix tables, and prevention tips to help you resolve misfire problems quickly and effectively.
Symptom – Cause – Fix Table
| Symptom | Likely Cause | Fix |
|---|---|---|
| Engine vibration at idle | Faulty ignition coils | Replace defective coils with OEM parts |
| Rough idle and misfires | Incorrect spark plug gap | Replace or regap spark plugs |
| Multiple-cylinder misfires | ECU injector signals or wiring issue | Inspect wiring, test ECU communication |
| Misfire in one cylinder only | Defective injector or coil | Test resistance, replace faulty component |
| Check engine light with P0300 | General misfire fault | Run diagnostics to isolate ignition/fuel |
Key Takeaways
- 1. Spark plug condition is critical: Incorrect gaps can directly cause idle vibration and misfires.
- 2. Ignition coils fail more often than injectors: Faulty coils are a common culprit in rough idling Mercedes engines.
- 3. Systematic diagnostics save time: By testing ECU signals and injectors first, unnecessary replacements were avoided.
- 4. Always use OEM parts: Non-genuine plugs or coils may not meet M272 performance requirements.
- 5. Test drives confirm repairs: Post-repair verification ensures long-term reliability.
Preventive Maintenance Tips
For Mercedes-Benz W204 owners with the M272 engine:
- – Replace spark plugs every 60,000 km (40,000 miles).
- – Inspect ignition coils during routine services replace in sets if multiple are faulty.
- – Use premium fuel to minimize carbon buildup.
- – Check ECU fault codes regularly to catch small misfires early.
- – Avoid aftermarket low-quality parts stick to OEM for reliability.
FAQs on Engine Vibration Idle in Mercedes
Q1: What causes engine vibration at idle in the Mercedes W204?
The most common causes are faulty ignition coils, incorrect spark plug gaps, or injector-related issues.
Q2: Can I keep driving with engine vibration at idle?
Not recommended. Misfires can damage the catalytic converter and reduce engine life.
Q3: How much does it cost to fix engine vibration idle?
- – Spark plug replacement: €200–€300
- – Ignition coil replacement: €300–€500 (depending on how many coils)
- – Major repairs (if injectors/ECU involved): €800+
Q4: How do I know if my ignition coils are failing?
Symptoms include rough idle, misfires under load, check engine light, and reduced fuel efficiency.
Q5: Can regular maintenance prevent engine vibration idle?
Yes. Timely spark plug replacement, ignition coil checks, and diagnostic scans greatly reduce misfire risks.
Author
Written by: Mercedes Expert
Automotive Technical Trainer & Mercedes-Benz Diagnostic Specialist
With years of hands-on experience repairing and diagnosing Mercedes-Benz vehicles, specializes in case-study-based troubleshooting guides that blend workshop accuracy with educational clarity.
Last Updated: September 2025
