This post is old as dirt, but I'd like to shed some light on running a K03 with K04 software. I recently upgraded from a ST Stage 1 to their Stage 3, which is the mild K04 tune without injectors. I have an 01, and have been running it now for 2 months or so. Within that time, I've never hit limp mode, bogged out, lost boost, etc etc....

Now, my car has 250K miles, and my turbo has recently started making the dentist drill noise, so a K04 is on its way. I left the stock 4BAR FPR with the K03, and surprisingly the Vag-Com revealed near perfect fuel trim ratio. It's odd IMO how the air/fuel ratio wasn't all jacked up since the tune didn't match the turbo, however maybe since there's less air flowing, the fuel amount was "doable?" Anyway, once I put the K04 in this week, I'll also install the 5BAR FPR that the tune calls for.

Again, during the 3 months I ran this setup, the car ran great, much improved power from the Stage 1 boosting 17-20 psi, and with the K04 programming was closer to 20 psi all around, however in certain RPM bands/gears would still only peak around 15 psi. I knew going into this setup with 250K on my stock K03, 170K+ on Stage 1......the turbo would be seeing itself out, just didn't think it would be within matter of months. Even though the turbo is making the loud drill noise, has been for about 3 weeks now, I haven't lost any power and/or boost...but by the end of the week, the K04 will be installed and ready to go.

Anyone have further questions, please let me know, would be glad to answer the best I can.