My 99.5 a4 2.8 cel came on about a month ago and the shop told me I needed to replace the #2 spark plug wire and oxygen sensor. I replaced all the spark plugs with platinum 2s and new bosch wires, oxygen sensor, air filter, oil&filter(10w30 pure syn-6 quarts) and it drove alot better for a week but now the cel came back and vag-com shows same fault codes(16684&16686) for cylinder 2 misfire and multiple/random cylinder misfire. Any ideas on what this may be? It seems to drive better since I replaced the wires ect. but still seems rough in first and second gear. Also it dosent seem to have as much power as it did before. I really need some help on this 1 guys.

 

I'm not that familiar with the 6, so take this with a grain of salt.

Problem seems to be centered around cyl 2, despite having changed everything short of ignition module/coil, which could be the problem. Could also be dirty fuel injector.

Clear codes and run some good injector cleaner such as Techron or redline and see if it comes back. If it does Try ignition module.

If you have vagcom with registered program, you can run output tests on the Evap system and injectors.