1999 Subaru Outback Wagon. Newly replaced spark plugs & wires. My knuckles have healed enough to type now. Runs great. Good mileage on a recent 1,000 mile trip. But at idle (like a stop light) there is a "stumble" every now & then... not consistent. almost disappears totally in neutral... the idle speed is low but can't see the how to increase that.