I am working on a TVS S197 Mustang GT/Tremec with LTs. Car runs great except for one issue. On decel, the car will occasionally overshoot idle. Idle is set for 800 RPM and only occasionally it will drop to 400-500 RPM and then recover. Although I cannot hear a misfire, I logged the car with two misfire PIDS; Total misfires since key-on and Misfire Detected (no/yes). When the car does overshoot the idle, I see an increase in Total Misfires (at idle only, not at mid throttle or WOT), but what has me mistified is the Misfire Detected PID always returns NO. Never does the Misfire Detected PID return YES. I am wondering if anyone can provide some clarity on these PIDs and suggestions on what to search for in the tune. Car has new plugs gapped at .025 and fresh COPs. MAF transfer is great. No significant IPC errors either.