newbie w/ turbo issues

[jdhartman24]

Greetings to all,
I'm looking for help, suggestions, criticism, etc. I have a 99 1.8t Passat w/110k miles. I have been having some turbo problems for the last month or two. Usually the car runs at full boost(8psi), occasionally however, I only get 5psi. There is no warning before it occurs, and it varies in how long it stays like this (30 seconds-hours) before it returns to normal. I just got the car back from service where they replaced a knock sensor saying that was the problem...they were wrong!:mad:. Here is what I have replaced so far, not related to this specific problem:
1. New N75 valve-1 1/2 years ago
2. Replaced stock DV with Turbo XS blow-off valve-2 years ago

Any help would be greatly appreciated.
Jason

[jdhartman24]

In looking at some other threads I thought maybe it was the MAF. I unplugged it and drove it, the problem is still there. Is it possible I have a small leak in a vacum line somewhere in the turbo? Any suggestions greatly accepted. :1zhelp: