A5 Misfiring: Plugs vs Injectors Troubleshooting Guide

As someone with moderate experience working on VAG engines, I had nearly identical issues with my 2015 A4. The symptoms you describe match exactly what I experienced, rough idle, engine misfiring, and poor throttle response during acceleration. After initial diagnosis, my workshop confirmed a defective fuel injector was causing combustion misfire in cylinder 2. The repair involved replacing the faulty injector and testing the remaining ones. Total cost was 515 Euro including parts and labor. While waiting for the repair appointment, I noticed increased fuel consumption and occasional jerking, especially when cold. The check engine light would sometimes flash during acceleration, which is typically a clear sign of misfire issues. The repair completely resolved all symptoms, smooth idle returned, power delivery normalized, and fuel consumption went back to normal levels. To help diagnose your specific case more accurately, could you share: Current mileage, When symptoms first appeared, Whether problems are worse when engine is cold or warm, If you notice any specific timing of the misfiring (idle, acceleration, or constant), Any recent maintenance history, Any diagnostic codes you might have pulled This information would help determine if your A5 is experiencing the same injector issues I encountered or if it might be related to ignition coils or other components.

Thanks for the detailed response. My mileage is at 96212 KM and last service was just an oil change about 2 months ago. The rough idle and combustion misfire started suddenly last week, mainly when the engine is cold. The check engine light came on right after I noticed the first symptoms. I did a quick scan and got P0301 and P0303 codes, suggesting multiple cylinder misfires. The throttle response issues seem worse in the morning, and the engine runs smoother after warming up. The fuel injectors have never been replaced, so your experience with similar symptoms is particularly relevant. Will get it checked at a shop this week, hoping its just a single injector like in your case.

Thanks for providing those details. Given the P0301 and P0303 codes on your A5, you're likely dealing with misfires in cylinders 1 and 3, which is similar but slightly more extensive than my single injector issue. The symptoms being worse during cold starts strongly points toward fuel delivery problems. In my case, I initially thought it might be just the one injector, but wish I had tested all of them since I ended up having another fail six months later. When the shop does your repair, strongly consider having all fuel injectors tested and possibly replaced as a set if they show signs of wear. It could save you from repeat issues. The rough idle improving after warm-up matches my experience exactly. This pattern typically indicates fuel injector deposits or deterioration rather than spark-related issues. My fuel consumption also normalized immediately after the repair. Based on your mileage and the multiple cylinder involvement, expect a repair cost around 800-900 Euro for a complete fuel injector service. While higher than my initial single injector fix, addressing all potential failing injectors at once is more cost-effective long-term. During my repair, I also had them check the fuel pump pressure since poor fuel delivery can cause similar symptoms, but that fortunately wasnt the issue in either of our cases.

Thank you for providing such comprehensive information about your past experience. Based on the P0301 and P0303 codes and symptoms youve described, I feel more confident moving forward with the repair. The pattern of cylinder misfire being worse during cold starts matches what you experienced, which really helps narrow down the likely cause. Im planning to have all injectors inspected as you suggested, rather than just replacing the ones currently showing issues. The higher initial cost of 800-900 Euro for a complete fuel injector service makes sense versus potentially dealing with repeated failures and multiple repair visits. Will schedule the appointment for next week and make sure they check the fuel pump pressure while theyre at it. The poor throttle response and rough idle have been quite concerning, so Im relieved to hear these symptoms completely resolved after your repair. Will update once I get the work done to confirm if my A5 had the same underlying issue. One final question, did you notice any improvement in fuel consumption immediately after the repair was completed?