Hello,
I'm rather intersted in DIY EGR tuning. None of my cars has got OEM EGR, so I collected some OEM EGR parts (Suzuki Swift, Daihatsu Charade). One day I'll weld in such a 'bypass'. The valve is feed by a vaccum switch typically.
A stupid 'controller' would just switch on/off (just for testing) in passengers cabin.
A more practible way would be to provide a PWM depending on load and rpm (and engien temperature).
I picked up also a Swift ECU which should do this. Should be enough for starting. At least I'll see under which circumstances engine runs leaner (less butterfly pressure losses in manifold) - when I dissable EGR from passengers cabin.
I see no disadvantage in bad exhaust - maybe sporty drivebility suffers - but that's not the main goal for eco modders, isnn't it?
»Horst