Bump for some more knowledge being laid down. I've got an '04 STi that has always run flawlessly - got tuned for E85 approx 5,000 miles ago and started misfiring in all cylinders about 2,000 miles back.
I've replaced plugs (which looked brand new w/10k on 'em) and did fuel filter today. Misfired within 30 miles. I'm cleaning the MAF tomorrow and then am looking at injectors as the culprit.
I did a compression check 10,000 miles ago and came in at 130 in all 4 cylinders. Plugs when pulled showed no signs of det and I'm tuned conservatively. The fuel is doing something, I just can't figure out what.