DD 74, did you fix your problem? I too am having this problem. It seems like everyone is pointing people to the 01 and above post for the fix, so I am assuming that I am on the right track, but like you I do not know where to start looking.
Here are some pics, someone in the know please let me know if I am in the right area (found a bad hose while I was looking around, will replace it and let you know if this works):
Edited out the img links, my name is hancoRck minus the R, and it is too dirty for this web site, so the links were not working, I will fix them when I have time. It looks like the vacuum hoses on the 99 are on the driver side of the engine (not sure someone verify please)
If we can get this sorted out maybe I can have these pics posted in that 01 link everyone likes to point people to, and we can at least drop the year down to 99 (maybe 98 I hear they are pretty much the same)
thanks for any help in advanced.