I disagree. A vacum leak would cause your car to idle terribly bad. Vacum leaks are not really extra air in the system. Vacum leaks are better described as false air.
My guess is a fuel pressure regulator, fuel accumulator, or a fuel pump going out.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".