Where are the resonance flaps on my W210?
 

I have read several posts on cleaning them but I am not sure where they are. They refer to the crossover pipe, but this car doesn't have a crossover like my 603.96 does. I see where the intake goes from the turbo to the intercooler, but then i'm lost. Does anyone have a pic? Any help is appreciated.

The turbo doesn't have them, only the N/A engine. In your car, the areas of concern are the intake manifold and EGR area...those can get rather gunky.

I'm having a hesitation problem on acceleration, should I try the EGR next? Or should this be a different post altogether?

I'm pretty sure you've already swapped vacuum transducers from turbo to EGR and confirmed both are working?

Have you checked that there are no exhaust/air leaks at the turbo? Next on my list would be pulling the IM/EGR assembly and making certain everything is clean (and moving freely) all the way back to the air filter.