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2017 C300 Rough Idle and Misfire Codes After Cold Start

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James R. · rep 0 · May 22, 4:11 AM · 1 replies · solved · Question

My 2017 C300 (W205) with about 70k miles has been acting up lately. When I start it cold in the morning, the engine idles really rough for about 30 seconds, almost like it's going to stall. The check engine light came on, and when I scanned it, I got P0301 and P0303, indicating misfires on cylinders 1 and 3.

After it warms up, the rough idle mostly goes away, but I still feel a slight hesitation under light acceleration. Fuel economy seems to have dropped a bit too.

I've heard about potential injector issues or coil packs on these engines. What could be causing this, and is it something I can troubleshoot myself before taking it to the dealership? I'm hoping it's not a major engine problem.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:11 AM

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ClearTheCode guidance (Mercedes-Benz · Engine & drivetrain)

Summary: For 2017 C300 Rough Idle and Misfire Codes After Cold Start, work through these steps on your 2016+ vehicle:

  1. Confirm the symptom — note when it happens (cold start, highway, after fuel fill, etc.).
  2. Scan codes — save all pending/stored DTCs; don't clear until you've recorded them.
  3. Check TSBs & recalls — look up your VIN for open campaigns and known fixes.
  4. Inspect the obvious — related fuses, connectors, fluid level, and recent repairs.
  5. Test the common fix — follow model-specific service procedures; one change at a time.
  6. Escalate if needed — burning smell, no brakes, overheating, or stalling in traffic → shop visit.

Owner reported: My 2017 C300 (W205) with about 70k miles has been acting up lately. When I start it cold in the morning, the engine idles really rough for about 30 seconds, almost like it's going to stall. The check engine light came on, and when I scanned it, I got P0301 and P0303, indicating misfires on cylinders 1 and 3.

After it warms up, the rough idle mostly goes away, but I still feel a slight hesitation …

This is educational guidance, not a substitute for hands-on diagnosis.

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