My SEC has been running perfectly until yesterday morning...I started it up, and it was running fine until about 5 mins into my drive I stopped at a light and made a U turn, and all of the sudden the engine started misfiring and shaking, the idle dropped to a little below 500RPM, and when I press the throttle, the car bucks and jerks and will barely accelerate. It seems like the farther I push the throttle down, the more the car slows. The engine sounds like it's trying, but the car doesn't really move.

My first thought was that it could be a vacuum leak, since I have had that problem in the past, but when I start the car, it runs fine for about 2 minutes, then the idle drops and it starts misfiring... any ideas? I ran it by my local benz specialist, and he basically just gave me a blank stare. Any help would be appreciated, since the car isn't driveable like this, and it's my daily driver...Thanks!

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Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles