1986 560sel, had badly fouled plugs, changed to fresh and now get a billowing cloud when idling in traffic. (haven't been driving it much since I changed the plugs)

Burned/used oil substantially previously and still does

Puff of smoke upon cold start and no smoke (begins to get slightly noticeable as car warms up... 60c onward) until operating temperature where it is visible from space.

Once warm, smokes at idle and under acceleration from idle for a few seconds... the longer the idle, the longer it takes to stop billowing afterward (within a 5 - 10 second band)

Doesn't appear to smoke at road speeds once undeway (possibly due to rapid dissipation)

Freeway driving fine except under hard acceleration (possibly due to even more rapid dissipation)

Any suggestions on how diagnose/troubleshoot to narrow things down further without pulling it apart would be appreciated with thanks in advance.

Patrick