... Now I've just got to figure out why it's not doing so on Turbo. Could that be the dual axis thing?
It very well could be. (Depending what you mean by "dual axis")
Turbo, at least in mame, uses a digital (aka on/off) switch pedal, while outrun uses analog pedals.
The above isn't all that important, except combined with three other facts.
- PC seperated pedals (dual axis accel & brake) default at one end of each axis
- Mame assumes every analog axis' default are the "center" of the range.
- When converting form analog device to digital input, less than center = one digital input and greater than center = other digital input.
So for example: the accel pedal outputs to Z axis, starting at zero when not pressed, increasing to 1024* as pressed all the way. Mame will assume the defualt of the Z axis is 512, and thus treat an unpressed pedal as pressing "Z axis down" if simulating a digital input (such as with turbo's accel).
Mame only runs into this problem when the pedals are on seperate axes. So you could set the driver to use "combined axis", "single axis", "joined axis" or "Y axis" pedals (different drivers call it different things), but this is usually hard to switch quickly (again depending on the driver) and does effect other games. If the pedals are in dual axis mode already, I'd try: enter mame's remapping UI (tab, this game), going to accel, half pressing both pedals
before next step, enter (to start remapping input), press the accel pedal all the way down (not quickly), return to center, and repeat for brake. It's worked for me before.
*BTW, the 1024 I used in this example is a valid number; 256 was a gameport analog limit, and if you have USB analog inputs the max limit is 4,294,967,295 (4GB!) per axis in windows. Of course, only the high quality devices go above 256 per axis.