From Matt:
When I asked about the speed sensor:
Not necessarily. When you break it down frame by frame it’s common to see the same RPM value for several frames, or even a later frame with a slightly lower RPM value shown. This is especially true with FWD cars because they’re usually near the limits of traction so every little inconsistency in the road is more visible than with AWDs. Going back to when this issue first occurred, I never saw a clear cause in the logs. I reviewed your latest log and your tune again. Fuel pressure is perfect, injector pulse widths are normal, AFR reading is stable, MAP and PUT sensor readings look fine, camshafts are in their commanded positions, fuel trims are consistent, etc. There are no hiccups in the RPM curve, boost dips, or AFR spikes which would be the typical indicators of misfire.
Do you actually feel or hear a misfire from the driver’s seat before the car throws the code and faceplants? Audible pops, maybe a “fish bite” feeling when a cylinder doesn’t ignite? The misfire detection is pretty good, but its not perfect. Occasionally (usually on built motors that are looser and therefore make more mechanical noise) the ECU will register noise / vibration as a misfire when there isn’t one. If the car feels silky smooth the then just faceplants with a misfire code, I have to wonder if there is actually a misfire, or if you’re getting a false code from unrelated noise/vibration. I see plenty of cars with actual misfires that never register a misfire code…it usually takes a significant and sustained misfire to trip a misfire code.