Car: 95 Z28 A4

Just recently this car started having some problems. About a week ago when I started it in the morning it was missing at idle and running very rough. I took my other car to work and when I came back and tried the Z28 again it ran fine, at idle and driving around.

It was OK for a few days and now it started doing it again. I was driving to work and it was running fine, and then it just started missing, both when driving and when idling at a light or something.

Where should I start with diagnosing this? First I was thinking about using a timing light on each plug wire to see if any of them aren't firing. If one or more of them isn't, first I would check that they were fully plugged in at both ends. Then maybe check to see if they got damaged or melted on the headers somehow (even though they have the heat insulating "socks").

Any other ideas I can try to pinpoint this? What if all plug wires are getting spark (timing gun lights up)?

 

Hmm... After peering around under the hood for a bit, I noticed this:



I guess it's hard for a plug to get spark through thin air The plug wire was still "on" it but it was so loose it fell off when I touched it. Don't you wish all ignition problems were this easy to fix?