Just a concept now, looking at a CIS injected car and options. I want to toss the CIS, install a programmable system and get cruise control in the deal. I DBW throttle body is probably in the mix but that is not a big deal either way. Surely someone has done this already please share your knowledge.
Drive by wire makes it a little tricky because the cruise is usually done in software.
But, if you want to end run the issue... Nedcar Volvo S40s (2004 and earlier, not 2004 and later) connected the cruise control unit to the accelerator pedal, not the throttle body. That may be worth looking into, even if it is just connecting your existing hardware to the pedal.
I had a customer with an Insight with aftermarket cruise installed, that HAD to have connected to the pedal.
To the best of my knowledge (have MS3 in a car), Megasquirt does not do DBW.
There is a DBW add on, but they're not going anywhere near cruise control with it. There are, however, standalone cruise control kits for cable driven throttle bodies.
If you can find an 80's BMW in the yard the cruise control is pretty much standalone with it's own harnesses and minimal inputs. The trickiest part would be figuring out what the speed output looks like from the cluster and emulating that (probably an arduino could do that), everything else is simple with an extra cable to hook up to your throttle body. I retrofitted it to my base E28 525i which was obviously easy as it came from an E28 so plug and play, any North American E23 7, E24 6 or E28 5 will have this stock, I'm guessing an earlier E32/E34 would have something similar
E28 cruise wiring.
Done ms with 80s/90s vw vacuum cruise. Works fine.
There are plenty of standalone aftermarket cruise control options for drive by wire. Plenty of people with base model cars that wanted it, especially in the 2008-2015 era.
I have MS2 on a ex-CIS Mercedes and the cruise works fine.
Car didn't come with cruise. But I want to add it.