I’ve a 02 outback 2.5ltr with 190K. I have had a similar problem usually related to cold, wet and when I park it outside in those conditions. Since I usually keep it in a garage it does not present much of a problem and I just live with it but think it would be major if I did not have a garage. Not sure what causes it; suspected cracked spark plug wires, changed them but no help. If it had an old fashioned distributor I would suspect a cracked cap, is there something in an electronic ignition that could act like a cracked distributor cap?