A couple weeks ago my '95 Legacy (EJ22) began running rough on a cold start, but only after sitting for at least 24 hours. Driving it daily seems to prevent this, but sitting over the weekend is enough time to trigger the rough running. Idling isn't too rough, but giving it gas to leave the driveway causes sputtering and stumbling. If I back off the throttle it eases up, but opening it up causes it to worsen and a misfire code to appear. The entire problem just goes away once my engine reaches operating temperature, but it's back the next day or the day after.
Any ideas? Never seen this before, but then again all my previous vehicles would just stop running completely instead of at least trying to run. ;)
-Matt