Subaru Repair: Missing engine, Subaru runs rough, Subaru check engine light

Question
I have a 91 Liberty (legacy) with the 2.2lt. It has an intermittant fault of an engine misfire. The plugs and leads have been replaced, so I am wondering if it is the coil pack? Do these things develop int. faults where one tower will not work or could there be something more sinister? Any help greatly appreciated.
Thankyou.

Answer
Marc,

If it is isolated to 1 cylinder, check the injector.  1990 to 1991 automatic transmission, with the grey colored injectors failed quite often.  Now keep in mind I am in the U.S. where the liberty is the Legacy and the above statement may only be true about the Legacy.  

From there I would suggest a compression and leak down test.  Really you can test or replace parts.

Justin