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2017 X3 xDrive28i Rough Idle & Misfire Codes P0301, P0303

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Christine P. · rep 0 · May 22, 4:04 AM · 1 replies · solved · Question

Vehicle: 2017 BMW X3 xDrive28i

Hi all,

My 2017 BMW X3 xDrive28i (G01 chassis, N20 engine) has developed a rough idle recently. It's most noticeable when the car is cold, but it persists even after warming up, though it's less severe. The engine feels like it's shaking more than usual, and I can feel vibrations through the steering wheel.

I scanned it with my OBD-II reader, and I'm getting P0301 and P0303 codes, indicating misfires on cylinders 1 and 3. The Check Engine Light is on and sometimes flashes under acceleration. I haven't noticed a significant loss of power, but the car definitely doesn't feel as smooth as it used to.

Could this be spark plugs, ignition coils, or something more serious like fuel injectors? The car has about 70k miles on it. Any common issues with the N20 engine causing these specific misfires? Thanks for your help!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:04 AM

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ClearTheCode admin answer:

The P0301 and P0303 misfire codes on your 2017 BMW X3 xDrive28i (N20 engine) indicate that cylinders 1 and 3 are not firing correctly. A flashing Check Engine Light signifies a severe misfire that could potentially damage the catalytic converter due to unburnt fuel entering the exhaust. This needs prompt attention.

Here's a systematic approach to diagnose and address the issue:

  1. Spark Plugs: Given your vehicle's mileage (70k miles), spark plugs are a primary suspect. Worn or fouled spark plugs are a very common cause of misfires. If they haven't been replaced recently, start here. You can try swapping the spark plugs from cylinders 1 and 3 with known good cylinders (e.g., 2 and 4) to see if the misfire moves.
  2. Ignition Coils: The ignition coils provide the high voltage for the spark plugs. A failing coil can cause intermittent or constant misfires. Similar to spark plugs, you can swap coils from cylinders 1 and 3 with other cylinders to see if the misfire code follows the coil. If it does, replace the faulty coil(s).
  3. Fuel Injectors: Clogged or failing fuel injectors can lead to a lean condition and misfires. This is a common issue on direct-injection engines like the N20. A fuel system cleaner might offer a temporary fix, but a failing injector will eventually need replacement. A shop can perform an injector leak-down test or flow test.
  4. Compression Test: Less common for sudden misfires but possible, low compression in cylinders 1 and 3 due to internal engine wear (e.g., valve issues, piston rings) would cause misfires. This is a more serious mechanical issue.
  5. Vacuum Leaks: A vacuum leak can cause a lean condition and rough idle, potentially leading to misfires, though usually, it would affect more cylinders or trigger lean codes (P0171/P0174).

When to See a Shop:

If swapping spark plugs and ignition coils doesn't resolve the issue, or if you're uncomfortable performing these steps, it's crucial to take your X3 to a BMW specialist. They have advanced diagnostic tools to perform injector tests, compression tests, and thoroughly inspect for vacuum leaks. Addressing misfires promptly is important to prevent further damage to the engine or catalytic converter.

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