If it does it at idle, or startup - I suspect valve seals allowing oil to seep past them to be sucked in on the intake stroke of one or more cylinders. But checking/replacing your PCV first wouldbe a step in th right direction. They are quite noisy and buzzy when the engine is first started in the morning. It will quiet down as the engine warms. Do a nice long, moderate climb up a hill at highway speeds and peek in your rearview for any clouds of smoke. Reverse course and drive down that hill with your foot off the throttle to also see if this induces some smoke. But grey-blue smoke at start up or idle may be malfunctioning PCV or valve seals that are gone. Neither is a huge job to do, thankfully.