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2017 C300 Rough Idle and Misfire - Check Engine Light On

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Mark S. · rep 0 · May 22, 4:13 AM · 1 replies · solved · Question

Vehicle: 2017 Mercedes-Benz C300

Hey everyone,

My 2017 Mercedes-Benz C300 (W205) with about 75,000 miles has recently started acting up. When I'm at a stoplight or in park, the engine idles really rough, almost like it's going to stall. It's also thrown a check engine light.

I took it to a local shop, and they pulled codes P0301 (Cylinder 1 Misfire Detected) and P0300 (Random/Multiple Cylinder Misfire Detected). Sometimes it feels like it's lacking power too, especially on acceleration.

Has anyone experienced this with their C300? Could it be spark plugs, coils, or something more serious like a timing chain issue? Any advice would be greatly appreciated!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:13 AM

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ClearTheCode admin answer:

It sounds like you're dealing with a common issue on the M274 engine found in your 2017 C300. While misfires can be caused by simple things like spark plugs or ignition coils, the symptoms you describe, especially with the P0300 and P0301 codes, often point to more significant problems.

Common Causes:

  1. Ignition System: Worn spark plugs or failing ignition coils are the most straightforward culprits. They can cause misfires and rough idling.
  2. Fuel System: Clogged fuel injectors or a failing high-pressure fuel pump could also lead to misfires and poor performance.
  3. Timing Chain/Camshaft Adjusters: This is a more serious concern for the M274 engine. Issues with the timing chain stretch or failing camshaft adjusters (phasers) can cause incorrect valve timing, leading to misfires, rough idle, and even a P0016 (Crankshaft Position - Intake Camshaft Position Correlation) code, though you haven't reported that yet.
  4. PCV System: A failing PCV valve or oil separator can create vacuum leaks or oil consumption issues that indirectly affect engine performance.

Troubleshooting Steps:

  1. Full Diagnostic Scan: A comprehensive scan with a Mercedes-specific diagnostic tool (like XENTRY/DAS) can provide more detailed fault codes and live data, which is crucial for pinpointing the exact cause.
  2. Inspect Spark Plugs and Coils: Visually inspect them for wear or damage. Swapping coils between cylinders can help determine if a coil is faulty.
  3. Check Fuel Pressure: Verify that the fuel pressure is within specifications.
  4. Listen for Timing Chain Noise: A rattling noise from the front of the engine, especially on cold start, can indicate timing chain wear.

When to See a Shop:

Given the potential for timing chain issues, which can lead to catastrophic engine damage if left unaddressed, it's highly recommended to have your C300 inspected by a qualified Mercedes-Benz specialist as soon as possible. They have the specialized tools and expertise to accurately diagnose timing-related problems and perform the necessary repairs. Ignoring these symptoms could result in much more expensive repairs down the line.

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