I have an '87 GN w/ a new motor, turbo, & tranny, etc. It recently started smoking out of the tailpipe if it is left idling for like 20 seconds. It doesn't smoke at all when driving or at WOT. While smoking I can rev it and it goes away. Looks and smells like burning oil. It is blue. Anyone know if this is a big prob. or something simple like valve seals or something?