I've been running a tweaked version of the NOTORIOUS VR Stage 2++ tune and I keep getting kicked in and out of limp mode. Any advice on where to start ruling out hardware issues and where to modify the tune is greatly appreciated!

Current Tweaks:  Bosch MAF, lowered LDRXN, Coded out rear O2's

I'm obviously overboosting and I'm also getting a big knock spike when limp mode starts. 

During one pull of this test run I had a flashing CEL but it didn't stay on. I hadn't checked or cleared codes in a while so I can't say for sure that these happened at the same time, but my guess is that the misfires in Cyl's 4-6 happened on that pull.  Here are all the codes (some don't matter):

18058 -  Powertrain Data Bus: Missing Message from Instrument Cluster
        P1650 - 35-00 -   -
17866 -  Exhaust Gas Temp Sensor 2 (G236): Short to Ground
        P1458 - 35-00 -   -
18014 -  Rough Road/Engine Torque Signal from ABS: Electrical Malfunction
        P1606 - 35-10 -   - - Intermittent
17869 -  Exhaust Gas Temp Regulation for Bank 1: Implausible Signal
        P1461 - 35-10 -   - - Intermittent
16684 -  Random/Multiple Cylinder Misfire Detected
        P0300 - 35-00 -   -
16688 -  Cylinder 4: Misfire Detected
        P0304 - 35-00 -   -
16690 -  Cylinder 6: Misfire Detected
        P0306 - 35-00 -   -
16689 -  Cylinder 5: Misfire Detected
        P0305 - 35-00 -   -

These graphs are over time so you can see when the limp mode kicks in.  I can't say that this log was for the same run that threw the misfires, but I could consistently get this to happen.

Boost and throttle position:


Knock - Note big knock spike at same time as overboost:



Thanks again for any advice you can give!

WGDC is logged in the csv file.  Here's WGDC on top of boost/time:



I'll try to get a log with the N75 unplugged in the next day or so. 

Thanks!

I believe the both "Exhaust Gas Temp Sensor and regulation" DTC`s was the problem.

These sensors breaks often.

In the last 3 years I have changed two sets (2x2) in my RS4.
In all these cases my car runs into limp mode.

17866 -  Exhaust Gas Temp Sensor 2 (G236): Short to Ground
        P1458 - 35-00 -   -

17869 -  Exhaust Gas Temp Regulation for Bank 1: Implausible Signal
        P1461 - 35-10 -   - - Intermittent

2nd notion of fixing egts (or coding them out)

Sorry. I missed the fact that you didn't actually throw a deviation code.

Misfires are probably from EGT enrich.

Limp is from EGT failure.

Overboost is (probably) unrelated to EGT - separate issue... like I said your PID needs some lovin.

That said, always fix the stuff you KNOW is broken first You never know what other problems will magically go away...

4-5-6 look a weak gasket on cover valve gasket , the rounds ones near spark plug