Today's update: The weather co-operated so I was able to get to work on removing the pedal from the E91. Unfortunately, this required drilling out the allen screw holding it in place. Foot-wells of cars where a lot of salt is used on the roads are pretty harsh environments.
After removing the pedal , I gave it a clean up and just for fun dismantled it to have a look at the circuit board . It was intact but the pin connections looked sketchy so I touched up the solder points. Upon re-connection, the faults remained the same.
I then took the time to remove the pedal from my E61 to see if it was possible to sub it in but quickly discovered that the connectors were considerably different so no joy to be had. I also spent some time looking through the live data options in BimmerGeeks Protool and was able to find the menu selections for measuring the voltages of the pedal, which I confirmed using the E61.
After re-assembling the E61, I proceeded to complete the process of drilling out the screw for the pedal on the E91 and re-tapping the hole.
Once that was done and the metal bits were cleaned up I used George's documentation as a guide to check the supply voltages to the pedal connector with the pedal absent. I confirmed that both ground wires were functional along with the pedal module supply voltages of 5 volts. This was done in key on, engine off mode.
I started the engine and cleared the codes, doing a re-scan and found that the throttle errors had disappeared with only the faults pertaining to the absent pedal being present. While the engine wasn't really happy, a check of the throttle pot voltages indicated that they were within spec. The idle smoothed out and eventually started to drop.
What this suggests to me is that one of the Hall effect sensor circuits in the pedal has failed as a short circuit which causes the ECM to then block off the corresponding input circuit of the throttle unit.
The next step is to try and source this unit: