It sounds like you are experiencing a loss of power, and this can be caused by the MAS, or even a failing fuel pump. These types of problems can be difficult and expensive to diagnose without the proper diagnostic tools and knowledge.
RepairPal Certified shops can diagnose and repair your 1990 Mercedes-Benz 300CE. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.