Hi! My Audi A4 2005 B7 has lost power and makes a whistling sound or similar to a siren noise (people have actually pulled over in front of me) when I put my foot down on accelerator. We've checked the turbo gate valve, waist gate (N75 solenoid) vacuum vanes are fine no leaks. Oil pump is fine squirts oil normally. We can't identify the source of the sound. Every time we remove vacuume pipe from turbo it goes quiet but we've taken the turbo apart and it's fine, its turning ok and not sticking. Anyone know what the problem is?

 

PCV valve? There is a recall for these on the 05 b7's. Have your dealer check your VIN.

 

What do you mean you took the turbo apart....?

The waste gate is internal and the flap door goes bad all the time. The only way you can tell is by removing the cat. It is very noisy and will cause a loss of power.

The breather may make a whistle sound but you won't notice a loss of power because it only deals in vacuum which is eliminated in acceleration.

I think the turbo is your problem. Especially if its chipped. These turbos don't handle much more boost over stock. I just don't think your checking it properly