Quick question - my car started shaking two days ago noticeably so I took it to Autozone for the diagnostic - secondary air pimp is gone which I had known about and misfire on cylinder 4 was no surprise because of the shaking - so I changed out the coil pack immediately - problem solved, shaking gone...not really - later that night it started again out of the blue...autozone said it was cylinder 4 again, and now ampther air pump problem, plus a torque issue - but I'm not as concerned about that as the misfire - I dont know if I have been driving on it enough for the codes to have changed. I pulled the sp, it looked a little dirty but not too bad...any ideas? is it possible for the coil to go bad brand new? or is it possible another cp went? Any ideas would be appreciated...

2000 s4