To be honest I'm not sure if yours is drive-by-wire or not but when I had a look I couldn't see an obvious throttle cable. Hopefully someone else here will have more of an idea?
If yours
is DBW the throttle alignment will have reverted to its default setting when you disconnected the battery to fit that jolly nice leather steering wheel you have. Take a look at
this thread. You mentioned you were getting poor fuel economy, even on a decent run, and this could be caused by your TB needing setting up properly.
If yours
isn't DBW then I'd probably start checking the mass air flow sensor for failure. I'm sure you should be getting better MPG, at least another 5-10MPG on top of the 28 you mentioned.
BTW any idea what model your steering wheel came from? It's much nicer than mine and I'm jealous!
DubSteve