Ok, lets assume for a moment that throttle can be modelled by a PID plant (it can't) - is the circuit temperature stable? You don't want the characteristics cha

Ok, lets assume for a moment that throttle can be modelled by a PID plant (it can't) - is the circuit temperature stable? You don't want the characteristics changing as the engine. Now you need a compensator circuit. What about power supply stability and noise? Car power busses are hella noisy, due to alternator and spark coil. Now you need some serious conditioning and filtering. What about knocking? Modern ECUs adjust parameters on knock detection to reduce the damage from pre-ignition. Gotta put in a control system for that. Repeat for manifold air temp, exhaust temp, emissions, rev limiter, etc., and as you mention, make that 3x for redundancy. Now you have hundreds to thousands of components, in a high noise, vibration, and temperature environment, and you have something which is about as efficient as an 80s car. And you can't as easily simulate it cause it's analog. Or just use some digital chips and simulate all the tuning.