Just for your info......
I have recently bought another coupe 2.2 SE1. When i looked at it, it was misfiring on 2 cylinders. Compression test (in 1-4 order) was 13bar, 11 1/2 bar, 13 bar, 11 1/2 bar.
I found that the timing had slipped 1 tooth at the crank cog. Both cam cogs were correctly aligned. After i reset the timing back to the correct marks at the bottom and top i done another compression test. All 4 cylinders were 12bar (+- 1/4 - 1/2 of a bar). I also replaced the single electrode spark plugs for the standard GM triple ones.
Result is now car starts on the key and runs like a dream!
As for yours i dont know why changing coil pack made a difference. But recheck your compression test and check your timing. This info may or may not help. :thumbup: