RustyBucket

Hi All. Just another data point for y'all. 1997 Subaru Legacy Outback 2.5 DOHC, Auto, 220K miles, original owner. Top end professionally rebuilt 7 years ago at 134k due to blown head gasket. Car has generally been very good with no other significant problems. About a 2 years ago and 20k miles ago, developed erratic miss, mostly at idle but also irregularly apparent at speed under low load. Swapped in new plugs and wires (no 2 or 4 [i forget] was singed at contact to plug). Problem solved. About a month ago again developed erratic idle miss. Doesn't happen when stone cold or until somewhat warmed up, more noticeable when fully warm and (for instance) sitting at a light. It is an sort of 'stutter cough'. 2 or 3 misses, then idle smooth for a few seconds, then a another little cough. Disappears as soon as RPM picks up, no hint of it at speed or under load. Checked plugs, they look good, and swapped in another fresh set of wires (thinking that #4 looked like it had what might be a burn mark from arcing across the face of the rubber boot between plug and plug well of cylinder). If had cured problem would have been $30 well spent. Problem persists. No idiot lights, no other apparent problem. Oil has been consistently changed every 4 to 7k miles for life of car. Burns/drips (gasket leaks) about a quart every 1500 miles now. Cali car, nearly always garaged. Need to get 3 more years out of her, that means at least 2 more Cali smog checks - so it'll need to be fixed by April at the latest. I could start throwing parts at it, or I can hand it to my mechanic with a blank check (they are good, but not cheap), but I'd rather just find and fix the problem - I've a sneaking suspicion it will be something insanely simple - but the car isn't really telling me what it wants. Any similar symptoms and what was your fix? Thanks.