Go to the parts store and purchase a cheap boost pressure gauge that has good reading down low. I think you are looking for 5-7 psi. If it is there, you have a fueling problem. It isn't uncommon to see clogged filters. (Your car has 3 fuel filters if you count the one in the tank) Also, I have upped the mixutre of the anaroid many times after a few years.

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Benzmac:
Donnie Drummonds
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS