Underboost P0299 and Intake Leak P2279 Mystery

[BEZMan]

Hi all!

I was looking for experience / advice from the community with my 2019 RS5. The problem I have started with a coolant leak and then a P0299 underboost code as soon after as I refilled the coolant the first time. Coolant continued to leak and it ended up being a leaking water pump. I got the pump replaced with the thermostat and coolant hoses, and also new breather hose and PCV pipe. Since the coolant had leaked into the charge pipe, and my mechanics cleaned that gooped up coolant.

I thought I was good and that the P0299 was related since it came up at about the same time..... not so fast. After a little while, the car started now to throw some P2279 codes at me: It almost does that when on idle. I would start my driving and boost seems ok (16 bars) and then after a while, if I come to a stop (traffic light) and idle, all of sudden it throws that Intake leak code at me - car goes into limp mode (no boost / turbo) until I restart it where it goes back to normal for a while. It is almost like clockwork every time I go for drive - drive some nomally and then error code and limp on first long stop.

I was going to do a smoke / leak test, but in the meantime, if anyone has had the same experience or have an idea where to focus our attention with my mechanics, that'd be great. Could this be coolant that had splashed on a sensor? Diverter valves? etc...

Thanks a bunch in advance!

[BEZMan]

I was driving this morning and pushed the car a bit after warm out, and all seemed fine - no code. After I parked the car, I left the engine running and poped the hood. I could hear a hissing sound coming from the PCV box area. I gently wiggle the breather hose and it appeared that the sound was getting stronger as did that, and coming from the connector between the PCV box and breather hose.

Question is: is that normal to leak air from there (hissing / leaking sound) - could this be a safety mechanism?

Breather hoses were replaced last week so could I have a bad connector?

2024-10-12_12-27-38.jpg

[jdm-v35]

O ring in that connector is probably not seated correctly.

[BEZMan]

O ring in that connector is probably not seated correctly.

Is that easy to do it myself or should I take it back to mechanics who installed it? If this is a 5 min on my end, I do not mind doing it but I saw some videos where it seems like you would break the hose trying that (and that you basically have to buy a new hose every time - could be wrong). Do I need some special tools to remove it or just some pliers? Thanks!

[jdm-v35]

Is that easy to do it myself or should I take it back to mechanics who installed it? If this is a 5 min on my end, I do not mind doing it but I saw some videos where it seems like you would break the hose trying that (and that you basically have to buy a new hose every time - could be wrong). Do I need some special tools to remove it or just some pliers? Thanks!

Pliers and maybe small screwdriver/picks. It is a PITA to remove those hoses sometimes.

[BEZMan]

Pliers and maybe small screwdriver/picks. It is a PITA to remove those hoses sometimes.

I am trying to figure out if my PCV valve has gone bad or the hose. I have disconnected (easy - just press the sides an pull - no tools needed) the hose and reconnected but the "leak" is still present. If I press the connector / hose again the PCV, it looks like it block the leak. I also notice that I have "suction" on the oil cap when I try to remove it. So there is vacuum in there. Last, there seems to be some light suction coming from the tiny hole on the PCV (as depicted on the attached picture). If I put my flinger to block that tiny hole, the engine start to get rough automatically. Is that normal to have that behavior on that tiny hole? What is that for?

The whole PCV + gasket + new oil cap is like $120 - at this point I am tempted to just change it (car is 2019 with 60k miles on it). It feels like it is quite straightforward with 6 screws. But not sure if my PCV is indeed bad.

Thanks again for your help / insight!

[BEZMan]

Update: second detachable connector on the breather hose (not the one connecting to the PCV) was not seated correctly and was twisting the connector on the PCV, creating leak. I removed the PCV, reseated that connector, put the PCV back and replugged the one on the PCV (now it plugs straight and firm), and all is fine now. Cars pulls great again and no code. The little hole still seems so sucky tiny bit of air, but I guess that is normal. Thanks all for the help.