Your vacuum gauge should be pegged full to the right at idle, warm or cold. If not, you have leaks in your intake. I wasn't sure based on your description. The vacuum gauge is a real valuable diagnosing tool that they removed on the later W124 cars.

__________________
http://i193.photobucket.com/albums/z...-RESIZED-1.jpg
1991 300E - 212K and rising fast...