I have an 03 a4 1.8t running stage 1. The last couple days my car has seem to lose a lot of power, the turbo spools fine but its very laggy before you start to actually feel it pull. Not sure what it could be I dont hear any boot leaks checked all my clamps and looked around. Could it be my diverter valve? im out of ideas any help would be appreciated.

 

It could be yes, do you have a boost gauge to verify spool and boost pressures?