So I just recently purchased a 2005.5 b6 s4 with the 4.2 v8. Love the car, but after having owned it for about a week, a code came up for a vacuum leak. I poked around and found a crappy hose repair job under the main engine cover. I got new line and connectors, then I cleared the code. Right after I did this repair, I went to go take a drive to see if the leak was fixed and if the check engine light would come back on. It did, but it would be flashing only over about 4500 rpms. My code reader said it was misfires on cylinders 1,5 and 8. So I pulled the coils and plugs to see that the plugs were 1: not the right plugs, and 2: disgusting. I purchased the correct plugs and new coil packs from FCP euro, and installed new valve cover gaskets while I was at it (they were leaking badly) then went to start it up, and it would barely run. Misfired more often than not. And it was all over the board. 5 out of 8 cylinders. I decided to make sure everything was good and tight just to be safe, then went to start it again. Let it run for about 10 seconds to see if it would work it out but no good. I then proceeded to put the old coil packs back into every cylinder that was misfiring. This fixed the problem when it was idleing. But the problem is still there whenever I put my foot down. Except after all this work it is only on cylinders 6 and 8 now. Tried swapping coils around. Still stays on cylinders 6 and 8. Even messed with the injectors. Still no luck.
I'm completely out of ideas on this one. Please if you have any ideas let me know! Also, could repairing the leaking vacuum line have anything to do with this? I'm new to this car and this motor and don't know what can make it angry.

 

so if anyone does have any ideas and sees this thread, I have an update on my situation. so after doing all the coils and plugs, I had no ideas. a friend of mine happens to have a VAG COM cable, and allowed me to borrow it for the time being. With the VAG COM, I was able to find out lots of other little things that were wrong with my car, but then I noticed, that all of the codes in all of the addresses, even a heated mirror, were all due to low and intermittent voltage. so after some time I have gotten around to replacing the alternator and voltage regulator (both the same component on most Euro's). I then proceeded to clear all of the codes with the VAG COM to run the codes again after running in briefly (it was still misfiring when I started it up after the alternator replacement). all the codes for low voltage were gone, and the only codes left were for the misfires. but I am out of ideas... please help