I've just replaced the EGR valve on my Audi A4 as it was limping on hills and had no power for overtaking. I replaced it with a cleaned used part. Unfortunately there is now a high pitch squealing sound at around 3k revs, there is a mark difference in performance but after around 10-15 seconds the squealing noise stops and the car goes in to limp mode again. Any suggestions on a solution would be welcomed.

Car Details
Audi A4 1.9 TDI diesel 130bhp - 127k miles - manufactured - 2001