Just to summarize my experience with the same problem:

After replacing the Mass air meter ($300-ish), and the throttle actuator ($1,400-ish), it was discovered that I had a vacum leak at the intake manifold gasket ($440.00).

I've learned from this forum that my kind of vacum leak is unusual.

If your problem is a vacum leak, there are other sources of vacum leaks that are more typical, like at the switch over valve at the front of the engine.

Mass air meter and throttle actuator failures are much more common.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".