Have a feeling I've made something worse by attempting to do something right 😞

Inlet manifold on my 2008 1.6TDCI was rather ropey; 2 of the lugs had broken off so it wasn't really sealing properly. Picked up another one from fleabay, cleaned it all out with a pressure washer & degreaser, left it to dry. Fitted it yesterday with new seals ensuring everything sealed nice and tight.

Now, everything appears to drive OK although a little sluggish in 4th but when accelerating or putting the engine under load there's a clearly audible whooshing sound you can hear from inside the car. I can't hear it when revving it from under the bonnet though. Checked as many hoses as I can find and all seem perfectly OK. Can't see any splits or holes and I'm certain the manifold has been correctly fitted. There's no fluid anywhere thankfully so I'm fairly sure it's air/exhaust gases.

I'd rather not leave it as it is in case something is more seriously wrong. Does anyone have any tips on what it might be? Not sure if it's related but I changed the manifold due to a P0428 error coming up recently and a mechanic colleague suspected the manifold. That error presents itself again after clearing the code.

There's also quite an amount of smoke coming from the rocker cover on the right hand side where I thought it should be drawing air in? (right hand side where the smaller of the 2 hoses connects from airbox)

Soapy water found it - the plastic pipey bit right above the DPF shroud - turbo boost pipe?

P0428 is the DPF temp sensor, not sure what that's got to do with the inlet manifold...

Yes the plastic pipe from the turbo is a boost pipe.  If yours is a 110, it splits on the left hand side between the intercooler and the intercooler bypass, if a 90 it just goes to the manifold, so you need to make sure the replacement is from the right power model.

He said something about airflow but I wasn't paying enough attention; I needed to change the manifold anyway as the lugs were snapped.

Now not convinced it was the plastic pipe, after using some gungum to seal around the bits I thought were blowing and making sure with some duck tape (classy stuff) I could still feel the air coming. May be a different thing completely as the turbo boost pipe was bubbling with the soapy water. The air is coming from the breather on top of the rocker cover; however really not sure if that's going to be the problem as I can't tell where the pressure is until driving 😞

Did the Gungum go off on cold parts?  It's meant for exhausts, the heat sets it hard lol.

Are the clips broken on the breather pipe?  Most are held on with cable ties now...  You will get some hot oil mist come out of there if the clips are broken, which can be drawn into the cabin and smell quite bad when driving.

Yeah, it's all I had that was suitable for high temps (as it's right next to the DPF shield, plus I used a heatgun to cure it 😄 )

It's a new breather pipe and that seems OK, the air is coming from the round bit just a little further back; looks like a removable cap but isn't removable.

Fair enough lol...  Tbf I had to substitute insulation tape for masking tape after breaking a wire on the brake wear sensor on Monday, ordered a new plug but the brake warning was driving me mad so had to bodge with crimps but couldn't find any proper tape haha!  

I think that cap is removeable, but not easily.  If the air is coming from there then you'll need to change the rocker cover.  I haven't seem them leak before though, definitely worth making sure it's not the breather literally 2mm away from it.