Hi All, My daughter's 2011 Mercedes C300 4Matic (110K) was difficult starting with the engine shuddering and check engine light came on. She shut the car off and started again and it ran fine. She said it happened a few random times in the past but the check engine light never came on and the car ran fine. I checked the codes and the following Confirmed/Permanent Codes were listed: P0300 - Random MisfiresP0305 - Cylinder 5 MisfireP0306 - Cylinder 6 Misfire Research shows it could be the spark plugs or coil packs. I am going to replace all the spark plugs. Should I replace all the coil packs at the same time or just Cylinder 5 and 6? The job looks fairly easy from videos I observed but the coil packs are pricey so curious if it was recommended to replace them all now? Any input on what parts to use? I looked them up on Rock Auto and FTC Euro and the price and brands vary greatly. Lastly any tricks to the install I might be missing. Thanks in advance. Bob K
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