Replacing a vacum leak is the cheapest of several options when diagnosing a fluctuating idle, but it is not the only thing to look at:

Generally speaking, a fluctuating idle can be caused by the following:

1. vacum leak
2. bad mass air meter
3. bad throttle actuator

__________________
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".