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Rough Idle and Misfires on 2018 911 Carrera S - DIY Spark Plugs?

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Sarah K. · rep 0 · May 25, 4:53 AM · 1 replies · solved · Question

Vehicle: 2018 Porsche 911 Carrera S

Hey everyone, my 2018 Porsche 911 Carrera S (991.2) has developed a bit of a rough idle lately, especially when cold. I've also noticed a slight hesitation under acceleration and the check engine light came on briefly, then went off. I scanned it with my OBD reader and got a P030X code (specifically P0301 and P0303 - cylinder 1 and 3 misfire detected).

The car has about 45,000 miles on it, and I'm wondering if it's time for spark plugs. I've heard the service interval for these is around 30k-40k miles for the 991.2. Is this a job that's reasonable for a home mechanic to do, or are there special tools or procedures I should be aware of for the 991.2 engine? Could it be coil packs too, given the mileage?

Any insights on tackling this would be great. I'm comfortable with basic wrenching, but haven't delved deep into the 911 engine bay before.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 4:53 AM

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ClearTheCode admin answer:

It sounds like you're on the right track with diagnosing misfires on your 2018 911 Carrera S (991.2). The P030X codes (P0301, P0303) directly indicate misfires in specific cylinders, and at 45,000 miles, spark plugs and potentially coil packs are prime suspects.

Common Causes of Misfires (P030X codes):

  • Worn Spark Plugs: The most common cause at your mileage. Plugs wear down, increasing the voltage needed to bridge the gap, which can lead to misfires.
  • Failing Ignition Coils: Coil packs can degrade over time, especially with heat cycles. A failing coil won't deliver enough spark to ignite the fuel mixture properly.
  • Fuel Injector Issues: Less common, but a clogged or faulty injector can cause a lean misfire.
  • Vacuum Leaks: Can cause unmetered air to enter the engine, leading to a lean condition and misfires.

DIY Spark Plug & Coil Pack Replacement on a 991.2:

This is a moderately challenging DIY job. While accessible, the flat-six engine configuration means working in tight spaces, especially for the upper plugs.

  1. Access: You'll need to remove the rear wheels and potentially the wheel well liners to gain better access to the coil packs and spark plugs.
  2. Tools:
    • Torx bits (for coil pack bolts)
    • Spark plug socket (usually 14mm thin-wall, 12-point for Porsche)
    • Various extensions and swivel joints
    • Torque wrench (critical for proper spark plug and coil pack bolt tightening)
    • Dielectric grease (for coil pack boots)
  3. Procedure:
    • Disconnect the battery (safety first!).
    • Remove the coil pack electrical connectors.
    • Unbolt and remove the coil packs.
    • Use the spark plug socket to carefully remove and install the new plugs. Be extremely careful not to cross-thread.
    • Install new coil packs (consider replacing them if they're original and showing signs of age, or if you suspect them as the cause).
    • Torque spark plugs to manufacturer specifications (typically around 23 Nm or 17 ft-lbs).
    • Reassemble everything.

When to See a Shop:

  • If you're uncomfortable working in tight spaces or lack the specific tools (especially a thin-wall spark plug socket and torque wrench).
  • If after replacing plugs and coils, the misfires persist, indicating a deeper issue like fuel injectors or engine compression.
  • If you're unsure about proper torque specs or the delicate nature of the components.

Replacing both spark plugs and coil packs simultaneously is a common preventative measure at this mileage, especially if you're already going through the effort of accessing them.

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