Q5 Misfiring + Rough Idle Points to Ignition Issues

Had similar symptoms with my Audi A4 2005 with the 2.0T engine. The rough idle and engine misfiring turned out to be failed fuel injectors. The throttle response was terrible, especially during acceleration, just like you described. The diagnosis revealed carbon buildup was causing the fuel injectors to spray unevenly. This created a chain reaction affecting the ignition coils and leading to incomplete combustion. When the fuel injectors are faulty, they cant deliver the proper amount of fuel to the combustion chamber. The repair involved replacing all fuel injectors and performing a thorough fuel system cleaning. This was definitely a serious issue that needed immediate attention, as continuing to drive with faulty injectors risks damaging the catalytic converter and other engine components. The symptoms you describe are nearly identical. While spark plugs and ignition coils could be the culprit, have a technician specifically check the fuel injection system. Make sure they perform proper diagnostic tests rather than just guessing at the problem. For accurate diagnosis, they should: Test fuel pressure, Check fuel injector spray patterns, Perform cylinder compression test, Scan for specific fuel trim codes

Thanks for your detailed response about the fuel injector issue. The symptoms sound exactly like what I experienced, the cylinder misfire, poor throttle response and check engine light matches perfectly with what my Q5 is doing now. I am curious, do you remember roughly how much you paid for the repair? Also, has everything been running smoothly since the fix or have you noticed any other problems popping up? Having a rough cost estimate would really help me prepare for what might be coming. My biggest concern is making sure I get this fixed properly before it leads to more expensive engine damage. I have already had to pay for several unsuccessful repair attempts with my mechanic who kept replacing spark plugs without solving the actual problem.

Glad to update on my A4 injector repair situation. After getting it properly diagnosed and fixed by a specialist, all the combustion misfires completely disappeared. The throttle response is now perfect and the engine runs smoothly without any jerking or hesitation. The total repair cost came to 515 Euro for replacing the defective fuel injector. While not cheap, it was worth every cent since the car has been running flawlessly for months now. No check engine lights or related issues have occurred since. Your concern about getting it fixed properly is absolutely right. Continuing to just replace spark plugs without addressing the actual fuel delivery problem will only waste money. The symptoms you describe point strongly to injector issues, just like in my case. Make sure your mechanic thoroughly tests the fuel injection system rather than making assumptions.

Back after getting everything sorted out. Finally took it to a different mechanic who actually listened and did proper diagnostics. Turns out you were spot on, it was indeed bad fuel injectors causing the rough idle and misfires. The new shop did a complete fuel system inspection and found two failing injectors that were causing uneven fuel delivery. Total bill came to 620 Euro including parts, labor, and a full system cleaning. Kind of steep but worth every cent since the car runs perfectly now. No more check engine light, no jerking during acceleration, and the idle is smooth as silk. Looking back, I wasted time and money letting the first mechanic keep replacing spark plugs without doing proper diagnostics. Really glad I found this forum and got pointed in the right direction. The combustion misfire issues are completely gone and the engine has all its power back. Lesson learned about finding a shop that actually diagnoses before throwing parts at a problem.