MAF Accuracy

How do I know that my MAF sensor reading is accurate?

Also how can I tell if my cam is too large for the current MAF sensor.

Provided the injectors are still stock then you can compare the commanded AFR to the measured AFR using a wideband sensor. If the MAF is accurate then the two should be the same. Be mindful that in closed loop mode the STFT and LTFT will correct any error so you need to take the trims into consideration, or better still force the ECU into open loop mode.

If the cam is too large then you'll struggle to get good control of the AFR at idle and generally struggle to make the engine idle stable.