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2019 E450 Rough Idle and Occasional No-Start

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Sarah K. · rep 0 · May 25, 3:04 AM · 1 replies · solved · Question

Vehicle: 2019 Mercedes-Benz E450 Coupe

Hello fellow Benz owners,

I'm having some concerning issues with my 2019 Mercedes-Benz E450 Coupe. Lately, it's developed a really rough idle, especially when starting cold. It feels like the engine is struggling to stay on.

On a few occasions, it's even stalled out after starting, and once or twice, it wouldn't start at all, just cranked endlessly. After waiting a bit, it eventually fired up. There's no Check Engine Light on right now, which is confusing.

Has anyone experienced similar symptoms with their E-Class? What could be causing a rough idle and intermittent no-start condition without triggering a CEL? I'm hoping it's something relatively simple.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 3:04 AM

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ClearTheCode admin answer:

Intermittent rough idle and no-start conditions on your 2019 Mercedes-Benz E450, even without a Check Engine Light, can be indicative of several underlying issues. Modern vehicles often store 'pending' or 'history' codes that don't immediately illuminate the CEL but can provide valuable diagnostic clues.

Here are some common culprits:

  1. Fuel Delivery Issues:
    • Fuel Pump: A failing fuel pump might not consistently deliver adequate fuel pressure, leading to rough idle or no-start. It could be intermittent as it struggles.
    • Fuel Filter: A clogged fuel filter restricts fuel flow, causing similar symptoms.
    • Fuel Pressure Sensor: A faulty sensor could send incorrect readings to the engine control unit (ECU).
  2. Ignition System Components:
    • Spark Plugs: Worn or fouled spark plugs can lead to misfires and rough idling.
    • Ignition Coils: A failing ignition coil can cause a cylinder to misfire, especially when cold.
  3. Air/Fuel Mixture Sensors:
    • Mass Air Flow (MAF) Sensor: A dirty or faulty MAF sensor can send incorrect air intake data, disrupting the air/fuel mixture.
    • Oxygen Sensors: While usually triggering a CEL, a slow or intermittently failing O2 sensor could affect mixture without an immediate light.
  4. Crankshaft Position Sensor: This sensor tells the ECU the engine's position and speed. If it's failing, the ECU might not know when to fire the spark plugs or inject fuel, leading to no-start or stalling.

When to see a shop:

  • Urgency: This issue should be addressed promptly, as stalling can be a safety hazard, and a no-start situation can leave you stranded.
  • Professional Diagnosis: Even without a CEL, a Mercedes-Benz specialist can:
    • Scan for pending or history fault codes using a professional diagnostic tool (like XENTRY/DAS).
    • Check fuel pressure and volume.
    • Perform live data analysis of sensors (MAF, O2, crank position).
    • Inspect spark plugs and ignition coils.

It's crucial to get a precise diagnosis to avoid replacing parts unnecessarily and to ensure your vehicle's reliability and safety.

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