Does your code reader show pending codes as well? How about freeze frame data? It's really hard to diagnose prior to a code unless it's pending or can be shown in freeze frames. The complexity of intake systems puts several culprits in the way - Crankshaft Position Sensor, Throttle Position Sensor (only it's not a TPS any longer, it's in the pedal assembly since it's an electronic throttle), MAP, variable valve timing and intake. I believe that any of those can create a pending code before they actually light up the CEL. Intermittent problems are the worse unless data is captured when it happens and you actually have something to show the shop.
