David Ramshaw

Hi, I'm new to this forum and hoping you guys can help me out. The engine in my bus came out of a 2001 legacy with a genuine 70k mileage. Recently, every time I try to start the bus, I don't touch the throttle, turn the key and she starts....on one cylinder! So, she pop pop pops away for about a minute then gradually other cylinders join in . At this point it is possible to feather the throttle a bit and then off she goes and from then on doesn't miss a beat. Anybody have any ideas?