Thanks David,

it is a 96 c280. The MAS was changed for a fluctuating idle a few years ago. Is the fuel pressure regulator a somewhat common performance culprit on this car? Do you have a part #? I looked up how a pressure regulator works. It says that it opens wide the fuel return valve when decelerating. Is a defective pressure regulator also the cause of a somewhat surging of the engine when coming to a complete stop? It seems to blip a couple of times as it comes to a complete stop. I posted this question before and others apparently have this problem as well. The website, of course, says this part is very simple and thus "rarely, if ever, goes bad." Finally, I have had a whining sound from the engine area when driving at freeways speeds.
After a while, when releasing the throttle and pushing the throttle there is a pitched whine upon applying and releasing the throttle. Could ALL my problems be a pressure regulator! Oh how I wish. Maybe it's responsible for my bumpy ride.... just kidding. Thanks.