Why CAN systems were adopted, High and Low, what a scan tool or scope can tell you, differentiating a bad module from a poor connection, and proper wiring/connector repairs.
Valve diameter, lift, and overlap are all contributing factors to the volumetric efficiency of an engine. If you can vary the relationship between the intake and exhaust valves you can broaden the power band and still have a smooth, clean idle. Variable valve timing is a great advance — as long as we can keep it working.
A pattern failure may indeed point you to a bad component, but when the part is expensive you want to be very sure it’s the culprit before you replace it.