Boost!! Up and down ??
 

Just watched the gauge while on boost hits a bar and drops slightly and then back to a bar,,and keeps like this? Why? I have no check engine light on while on boost?

what dump valve have you got?

sounds like you have a boost leak

I get this a bit too. Someone told me it could be the neutral position switch faulty. As when the car thinks its in neutral, it drops the boost down. Don't know if it's true or not?..