The Mx00 series ECUs can only control one DBW throttle, and you need the DBW4 if you have more than one.
There is more to a DBW throttle than a simple PID. It has a two separate throttle position inputs that need to track each other for safety -- these need to be confirmed as well.
I happen to have a perfect condition used DBW4 for sale if you need one. Smokin' deal available.