Not sure if this applies, as I'm not an expert on the 3800SC (yet
) Something to consider might be the PCV system. On a Non-SC car, that might be a symptom of the PCV valve sticking open. Like I said, just don't know how it works for the SC version, but maybe others can chime in and educate us (me)!
'87 GT in process, including GA / Seville brakes, Poly Suspension, '95 3800 Series 1 SC ( 225 hp ) T460e.