I've been having problems with my Subaru, it pings when I'm driving but not during hard acceleration, or when climbing a hill. Typically only when I'm driving at a steady speed, in all gears. Sometimes when I'm slowing down and then when I give it a slight amount of gas, it pings and blows out a cloud of blue smoke. Can some one help me narrow down the potential problems? It's a 1.8L F.I. non turbo, with a three speed a/t. I don't want to start tearing it apart until I have some idea what the cause could be.