iif using the auto ecu it cant see the signal from the VSS (speed sensor) makes them stall a bit and drink the fuel bad error codes will be shift solinoids etc all the trans codes.you can repin the ecu plug to a vn ecu if you cant find a vr manual ecu which are getting hard to find and it will help with the idle etc its relativly easy but not a job for the faint at heart few wires need adding for extra earths and power but it is relativly easy
the vr and vs are a bit different pin wise for swapping c5 to d2 as the vr auto doesnt have the manual vss feed in them.it requires a full repin of the plugs to suit the new ecu VS would be even worse to do but doable for sure would have to add MAP sensor and join all the injector wires so they fire at once
I only did my convo a few months ago (auto to manual) and i just rigged the speed sensor to work but i have had no problems with the idle or excess fuel usage. Is it really necisary to change the computer??? and if i did would it be plug and play or would the whole loom need to change also????