I sure am glad you guys are talking about this subject as my 89 420 does the same thing but only slighly and about 10-20 seconds max. Then smooth as a whistle. Its a little annoying but not to the point of seriousness yet.
My mechanic told me its probably a leaky injector, but now I'm wondering as it hasn't been checked yet. With 105,00 miles I would think injectors would be O.K> but you never know.
Will keep up with your verdict. Thanks for the new light shed here.
1989 420SEL 105575 miles
1990 Chevrolet E-Cab C-1500
1989 Olds Toranado Trofeo'