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Rough Idle and Misfire after DIY Spark Plug Change on 2022 330i

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Mike T. · rep 0 · May 22, 4:09 AM · 1 replies · solved · Question

Vehicle: 2022 BMW 330i (G20)

Hey guys,

I just changed the spark plugs on my 2022 BMW 330i (G20, B48 engine) myself this past weekend. I followed a few YouTube tutorials and thought everything went smoothly. However, ever since, the car has a noticeable rough idle, and I'm pretty sure I'm feeling some misfires, especially at lower RPMs.

I used the correct OEM-spec plugs (NGK Laser Iridium) and torqued them to spec. I'm worried I might have messed something up. Could it be a coil pack, or did I perhaps not gap the plugs correctly? I didn't check the gap as they were supposed to be pre-gapped.

Any ideas on what to check first? I'm getting a little nervous driving it like this.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:09 AM

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ClearTheCode admin answer:

It's frustrating when a DIY job leads to new issues, but a rough idle and misfires after a spark plug change on your 2022 BMW 330i (G20) are common symptoms that can often be resolved with some troubleshooting.

Common Causes & DIY Checks:

  1. Coil Pack Connection: The most frequent culprit is a coil pack that isn't fully seated or properly connected.
    • Carefully remove the engine cover.
    • Inspect each coil pack. Ensure they are pushed down firmly onto the spark plug and that the electrical connector is securely clipped into place. Listen for a distinct 'click' when reconnecting the electrical harness.
  2. Damaged Coil Pack: It's possible to accidentally damage a coil pack during removal or installation, especially if they are older and brittle. Look for cracks in the plastic housing.
  3. Incorrect Spark Plug Gap: While many spark plugs are 'pre-gapped,' it's always best practice to verify the gap, especially for sensitive engines like BMW's B48. Even a slight discrepancy can cause misfires.
    • Remove the plugs one by one and check the gap with a feeler gauge. Refer to your owner's manual or a reliable service manual for the exact specification.
  4. Incorrect Spark Plug Type: Double-check that the NGK Laser Iridium plugs you installed are indeed the exact part number specified for your 2022 BMW 330i B48 engine. Using the wrong heat range or design can cause issues.
  5. Debris in Cylinder: Less common, but ensure no debris fell into the cylinder during the plug change.
  6. OBD-II Codes: Connect an OBD-II scanner. You will almost certainly have P030x codes, where 'x' indicates the cylinder number experiencing the misfire (e.g., P0301 for cylinder 1, P0302 for cylinder 2, etc.). This will help you pinpoint which cylinder to focus your inspection on.

When to See a Shop:

  • If you've checked all connections, verified gaps, and confirmed the correct plug type, and the misfires persist.
  • If you suspect a damaged coil pack and don't have a spare to test with.
  • If the misfire is severe, causing the engine to shake violently, or if the 'Check Engine' light is flashing (indicating a severe misfire that could damage the catalytic converter).
  • If you're getting multiple, random misfire codes (P0300) that aren't resolved by the above steps, as this could indicate a deeper engine issue.
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