If you use an 8026B, you'd be able to read true RMS voltage (but not frequency). At idle RPM, you should read about 400 Hz at the cam sensor and about 2K Hz at the crank sensor. The P-P voltage will be about 5, but the RMS would be really, really low. You can performs the check about the same way you did, with the POS lead on the BRN/WHT wire (J terminal) and NEG lead on the RED/BLK wire (M terminal).
When checking the cam signal output (F terminal) reference the meter to the K terminal (signal ground).
You should also meter resistance or conductivity between the K, L, and M terminals. The ICM is grounded only through the base, and corrosion and decomposition of the heat sink compound on the base and its fasteners can prevent a good ground, and therefore, good ignition signals. I've had a few of these for which I've had to remove the coil packs, ICM (module), and scrape/polish the base to get a sufficient ground, after which all problems went away. Don't forget to apply a fresh, thin layer of heat sink paste to the ICM/base when you mount the ICM.
And when all is well with the ignition system, you're still likely to have an oxygen sensor error.