This one is for the archives, because anyone searching for "boost" or "negative deviation" will definitely come across my multiple posts and I think that my solution may be somewhat unique.

I chipped my car (GIAC) a few months ago and then went about fixing all the components that weren't able to handle the new boost levels: DV, N75C, L hose, etc. I eliminated all other DTCs by replacing front & rear O2 sensors, MAF and knock sensor 1 but was still plagued by a negative deviation code.

I pressure tested the intake side and found no leaks. I individually pressure tested all the components on the vac side of the intake manifold and replaced a leaking SJP but was still getting the DTC and being thrown into limp when driving hard.

I logged and graphed every block out there and tried to find something that would provide a hint. Posters suggested all kinds of things, including that my turbo was shot (incidentally that was all that Bentley's had to offer after all the successful tests, but they weren't dealing with 18+ PSI on a K03.)

I installed an APR turbo inlet hose thinking that it might be collapsing. KTR, in consultation with Jeff Moss who flashed my car at the NE GTG @ KTR, suggested that the cat was clogged, melted or somehow restricting airflow in an abnormal way. They disconnected the cat from the DP and it looked fine. They didn't have the turbo <> cat gasket in stock so weren't able to check that side so they ordered the gasket and I made an appointment to return.

Deciding that if the cat was fuxored I would need to replace it and a HFC is never a bad idea, I bought one from Labree Motorsports (400 cell ceramic) along with gaskets, studs, nuts & bolts from 1stvwparts.com and just had it installed this morning.

I was disheartened upon examining the old cat - it looked fine to the naked eye from both front and rear - no obvious issues with the substrate surface on either end. It looked like the theory about the substrate having melted was wrong and we would be going back to the drawing board.

Driving home I could feel a difference and decided, on a whim, to see if I could get the car into limp mode by driving hard in third (and the accompanying negative deviation code). I dropped into third gear on an onramp and ran from 2k RPM to redline/WOT. No limp. Hmm, pulling off the highway, I circle around and get on a ramp again - second gear would always throw it into limp too when I went to redline - again 2k RPM to redline/WOT and again, no limp mode, just nice powerful boost.

This weekend I will do some VAG COM logs (115/119) but at this point I can't make my car go into limp mode when it would readily go in prior - so I THINK IT MAY BE FIXED!!! YES!!!!

Now if I can only figure out how to resolve the "gear hunting" when I floor it in 5th gear ...

Thanks for everyone who contributed along the way. I guess it has been a good experience because, although I'm still a noob, I have learned a lot about my car along the way.

 

i'd cut the old cat open to see what exactly is wrong with it.

 

I have the Tip Chip and my car doen't hunt around..... the price is pretty reasonable too. I picked mine up from AWE. It would be worth a look anyway.

 

Hey I have a S4 Tip and have no gear hunting problems at all.

Im using an OCT Tip chip matched with their stage 2 chip.

They recommend getiing both chips from them. I dont know since your ECU is already chipped if they will suggest using their TIP chip.

I too now though have a negative deviation code which means the car is overboosting.