I have a built LS engine that has recently begun to idle rough. It was tuned using Hondata S100 a year ago and has run as expected since then. Could this be a vacumn line, idle valve or just time to re-tune?

Build included ITR pistons, new valve train with Crower 404 cams.

Thanks,

 

Re-tune should be the last step. You'd get a CEL indicating that the ECU had failed the self-diagnostic at startup.

Check for vacuum leaks (PCV, evap emissions, etc.); while you're in the neighborhood, inspect the IACV.

 

Thanks for the help!