I’ve 2005 Subary Forester automatic with 2.5L engine. It ran fine since I purchased it in 2005. However for the last 3 months it is behaving strangely. When it sits in the garage for 2 days or longer, it starts up very rough. It feels like the engine is misfiring. If I let it run for 10 to 15 minutes, it is back to normal!! The car has 80,000 miles. It was tuned up at 61,000 miles. I recently had a diagnostic check done. It showed no problems.
Next time the car sits for a few days, try this:
Turn the key to "ON," wait five seconds (count slowly), then turn the key to "START."
Let us know if that makes a difference.