Difficult Cold Start

I am asking you some help concerning a start up problem on a friend of mine's 92 vert.
The car has 55k and when cold the start up is succesful at first shot but then the car runs rough like some cylinders were not active.
After a few seconds the engine runs good and a start when the engine is warm is no problem.
The spark plugs were changed a few month ago so do you think this might be related to a dying optispark ?
Thank you for your feedbacks.
Greg



