Audi Repair: 99 Audi A-4 Misfire, spark plugs, spark plug

Question
The second cylinder from the rear of the engine is misfiring.  I've replaced all of the spark plugs and replaced the ignition coil with no luck.  I'm sure it's this cylinder that's misfiring through trouble shooting and the smell of unburned gas when remove this particular spark plug. I've also checked the wires in the dark to see if there was a spark from a current leak but didn't see any. I've heard that a cylinder 2 misfire is caused by a bad Ignition Control Module (ICM) but want to make sure before I buy one for $150.  Is there any other reason that this particular one would misfire other than a bad ICM?  Thanks

Answer
Hi there,

a misfire doesnt necessarily mean a faulty ignition system. a compression leak can also cause a misfire that mimics an ignition misfire.

have the compression measured and compare with all the cylinders, the maximum allowed differance between the cylinders is 3 bar.

Also worth a try is to swap the injectors around and see if the misfire moves with it.