Let me start by saying I'm not the best tuner the planet has ever seen, but I have tuned well over 1,000 cammed C5's in the last 20+ years. In the last 6 months to a year I can no longer tune a 411 PCM, or any C5 for that matter with an EFI OS. None of the cars will idle, terribly inconsistent, basically undriveable. No issues anywhere else in the tune. I am talking 20 or so cars now that I have fought with for days.

The only fix is to wipe out the EFI OS and tune it with HP, then the car runs perfect. (and I hate using HP)

Am I the only one having this issue? I have such a huge library of C5 tune files and now I have to tune each car by hand, writting files in HP. Besides the cost, did I mention that I hate using HP?

Any help would be appreciated, thanks.