Yes, before my mech friend found the neighbor’s MAF defective, the neighbor had replaced the battery and the alternator. The voltages were good, steady.
All of the computer and control sensor circuits require a steady 5V which come from battery and alternator. Voltage regulators in the electronics should be keeping a constant 5V but volt regulators can go erratic over time especially with a degrading battery or alternator.
The bigger picture I see is that computers, computer circuits, computer sensors, placed on automotive engines can help fuel and emissions issues BUT ...
by placing such systems on an automotive engine and drivetrain, IT INTRODUCES LONGER TERM SAFETY CONCERNS.
My engineering brain tells me that automotive engineers should design a bypass of all electronic controls FOR SAFETY PURPOSES.
If a situation arises where a vehicle system is IN BYPASS meaning the system has determined the computer control system has a fault, then a design can be added to turn on a light inside the dash display and turn on a flashing light outside. This allows the driver to drive safely while getting the vehicle to a shop to investigate the electronic control system.
To have a vehicle shut down in hazardous conditions because of electronic malfunctions or conditions IS INTOLERABLE and especially when those systems exist to control fuel and emission performance which is a noble goal but which is secondary to safety.
Safety comes first.
I am informed that a ‘LIMP ALONG’ system is sometimes included in these control systems meaning that the vehicle can be driven a short distance but that this is related to security and not fuel/emissions and which does not resolve the safety concerns.
Uh... wow. You have little idea how modern vehicle electronics or system controls work.
The alternator is supposed to output a steady nominal 12V (in actuality, soemwhere around 13.8-14.5 to charge the battery and run all the systems in the car at the same time.) 5V would not run the car’s electrics, let alone electronics. 5V is provided to the sensors and only the sensors via voltage conversion in the car’s computer module - however, not all cars use a 5V baseline and many use 12V instead. One reason 5V is used is because this was inherited from the computer industry - your typical desktop computer of the 1980s had a power supply that provided 12V and 5V for various technical reasons and with the addition of 3.3V this continues through today.