UrS4 full boost engine cut at high RPM
 

I have an issue that I've been chasing for a while. Under load, say 3rd or 4th gear, WOT and 5000+ RPM, the engine will cut back abruptly. When this happens, there is a noise from the turbo/air box area heard from inside the car. The car has Lehman 280 hp chipsets installed, stock wastegate spring (took 1.9bar out-seems to happen more often), new N75 boost valve, bypass valve was replaced before (had vacuum leak), new fuel pump and spark plugs. stock UrS4 manifold, turbo and exhaust. Ignition system is fine, as its never had a misfire and pulls hard all the time. Wastegate was vacuum checked for leakage, none. Also, the wastegate spring perch has never been touched either. IMO, it feels like the car is having boost surge spikes, but I'm not sure as I really don't have another car to compare it to. Also add, the mass air flow is new also (RS2 mass air meter). Vehicle has no air leaks when I checked last and also has the Samco Michelin man hose installed at the intercooler. Anyone have any ideas of what to look for or check?? Also, is it normal to hear a turbo spooling like hiss noise at part throttle? I've always noticed that, but if you get into the thottle right then and there, its still needs to build up boost it seems before it really gets going. I'm starting to wonder if the chipset programming could be the problem and if anyone else has had this issue. TIA!

Too many clues/variables. Start with a boost leak test. Try this post for clues:

https://www.audiworld.com/forums/sho....php?t=2173704

When you are done, report back.

Didn't do any pressure leak tests yet, but was doing some extensive long test drives today in the heat (100+ miles round trip) to make sure the new fuel pump installed cured the stalling issue. That seems to be rectified, but I also noticed today that it wouldn't act up anymore on full boost, even at WOT at low RPM's. It did though have the MIL come on after pulling off the highway at a red light and had no boost during that time. That issue went away after a key cycle off/on after refueling, so I will have to check for any new DTC's that may have been stored after that test drive. Will check for pressure leaks this week at .5 & 1.0 bar to see if any exist. I will have to locate the VW/Audi pressure tool to see if I have it or test it with the dealers tool. It may also have been a adaptation of the N75 that the ECU had to relearn once clearing the DTC's yesterday. Will post back what I find shortly.

Pressure testing the intake tract for boost leaks
 

is done with a homemade pvc plug for the turbo outlet hose to apply compressed air. I have
never heard of a VAG tool for this job.

There is a VAG tool. Its a aluminum cone with different diameter lips and has a air line nipple screwed onto it. It comes with a large rubber hose and a small hose with block off plug for the breather system. It came out when the 1.8T engines were released. Then there is the pressure check and leak down gauge that came out originally for the Corrado G60 and some plates that you can use to block off the thottle plate hose. You could use the breather plug to block the ISV hose if your just testing for leaks from the turbo to thottle body only.