Help needed 1.8t power lose after 60mph?!?

Hey guys newbie here and it brings me no pleasure my first post being so negative but I'm looking for some help and Audi experience.

For a while now (2 months) I have been experiencing a power loss in my A4 1.8t cab 2003. The car seems to drive fine at a normal steady pace around town and so on. Once you step on it 60mph plus.. The car seems to lose power.. And has a jerking effect under acceleration. The car will still build up speed but with the throttle fully open the car seems to let off.. Then pick up again and then let off and the pick up again.

I have popped the bonnet and there does seen to be a hissing sound from some of the vacuum pipes above the intake manifold not far from the pcv. Starts up fine, idle seems fine and sounds fine from the back (exhausts). When the car is idling at running temp and I remove the engine oil filler cap there is a pound noise which doesn't sound right at all. I can also hear an echoy type noise coming from inside the air box.

Also a few days ago my EPC light came on.. I arrived home parked the car. Returned to it the following day and the light don't come back on. Today on the way home in exactly the same place the EPC light reappeared. The light has now gone off. Could this problem be a failed PCV valve?

Sorry for the essay, but any and all help would be appreciated

Thanks for the speedy reply Karl210. Looks like you've crack it lol, will have a look for a new one one online.

Can I also ask, do you know if the a4 b5 inlet pipe is the same as the b6?

Thanks guys, quick up date. Found what I thought was an air leak. Went to change the pipe today and removed the ducking for the air filter and saw that the crank breather wasn't connected to the air box what so ever!! Don't know exactly what this can cause. Reconnected it and can't hear what I thought was an air leak now. Sprayed some soapy water around the area that was hissing and nothing.. Going to go for quick road test now to see if it boosts.

I did notice a sensor/valve just above the air box that was.. Ticking if you like. Could be normal but not really notice it so that could be due to reconnecting the breather pipe.

I will try to include a picture with this valve circled. Not sure if it's the N75? Would like to know what it is any way if anyone can shed any light on that. Thanks guys