I can't help on this specific application, but fly by wire throttles we do see a lot, most have 2 circuits for plausibility and redundancy - to be sure the input is valid!
Most, but not all, of the dual circuits work in inverse so (and using Tangoman's circuit as the example - which shows it set up this way with opposing sliders on the potentiometer) - I'll simplify by saying 0.5 to 4.5v but this might be 0.3 to 4.8v, or something else, and might be not inverse, both might be rising, however the picture shows a common supply, so lets expect a directly proportional inverse. So here you go:
- Output A = 0.5v at idle and 4.5v at WOT - Pin 1 at pedal, Pin 10 at the ECU
- Output B = 5v at idle and 0v at WOT - Pin 5 at the Pedal, Pin 29 at the ECU
Your pedal (if this is the correct wiring for your vehicle) has another 2 circuits, that are ground switched to show Idle and WOT:
- WOT - PinB at Pedal / Pin 30 at the ECU
- Idle - Pin D and Pin 8
So 4 Circuits ... Assuming you have a 4 channel scope I'd personally check at the ECU first, as this validates the wiring harness, and then recheck at the Pedal - but access might be an issue and therefore going to the pedal might be more pragmatic in this instance, so I'll explain what my approach would be...
1st test - at Pedal for ease - Key On, Engine off - We'll assume that the ECU supply (pins 33 and 30/8), wiring and earth (51/50) are good for now.
Timebase - 500ms/div / Sample 50ks
ChA - +/-5v - Pin 1 - expect near zero volts at idle rising to near 5v at WOT
ChB - +/-5v - Pin 5 - reverse of Channel A 5v dropping to 0v
ChC - +/-20v - Pin D - Idle switch - expect circa 0v at idle and 5v (might be 12v or 1v) when not
ChD - +/-20v - Pin B - WOT switch - expect voltage (similar level to ChC when not at idle) until WOT when it should be reduced to 0v
Make sure you use a Chassis earth on one channel - not Pin 3 or pinA or PinC!
+ Create a maths channel to be A+B - this should show an almost flat line at circa 5v, critically, it's going to be almost dead flat, and much easier to see incongruous data as spikes here, and this is in effect what the ECU is doing to valid the two position readings. If you had a dual rising signal you could attempt to create a flat line comparison using a maths channel like this, for say a 5v chA and 2.5v chB = "A-(2xB)" or even some offset adjustment "A-(2x(B+0.2))" but you'd need to play with this!!
Start the scope capture and then at various speeds of pedal movement - from slow and steady and slow steady release, to rapid snap, depress the accelerator pedal several times. Some part depression and release, might help if the problem needs to be provoked, but start off with simple full open and release.
This will get you a very quick idea of the function of the Pedal, and provided the chance to adjust the scales, arrange the data/scaling to give a screen that you can analyse. If ChA/B are "over limit" then change them to +/-20v
If the ChC and D appear to be working, then I'd drop them and re-use the channels to study the earth and supply of the potentiometer:
ChC - +/-5v - Pin 4 - ECU Supply +5v should be expected (again might be over limit so +/-20v)
ChD - +/-1v - Pin 5 - Earth 0v over very close
Retest, and see if these values have any "issues" (drops/spikes) that correlate to any "issues" at channel A or B
If you see nothing after either of these tests with engine off, the try repeating the test engine on, or in deed on a road test.
Personally I'd then clean and VISUALLY inspect all the connectors with contact cleaner and GEL then with a dielectric gel (Pedal, ECU and any other joints between the two) and retest, we see lots of issues due to high resistance on connectors, or with wires pulling at the pins from mechanical strain - being kicked etc!
At this point if you still don't see any "issues" then retest at the ECU pins, which will also test the wiring harness and show a more realistic picture of what the ECU is seeing (possible signal being earthed due to wiring issues etc).
ChA - +/-5v - Pin 10 - expect near zero volts at idle rising to near 5v at WOT
ChB - +/-5v - Pin 29 - reverse of Channel A 5v dropping to 0v
ChC - +/-5v - Pin 33 - ECU Supply +5v should be expected (again might be over limit so +/-20v)
ChD - +/-1v - Pin 51 - Earth 0v over very close
Again earth one lead to chassis, not an ECU earth.
Attention to volt drop verse the pedal readings taken earlier, especially on the earth and supply ...
Of course most modern diagnostics tools would allow a rapid solution by doing a "recording" of the values that it (the ECU) is seeing -both the throttle pedal parameters and both switch status ... which is where I would have started, but it's not as much fun as getting the scope on the car!!
The Diag Tool would not confirm if the fault was the ECU 5v output (ECU rebuild/renew), or a poor earth (probably the external earth connection, but could be internal to the ECU), or the Pedal verse the wiring. BUT would have given you some guidance and help as to what elements needed to be focussed on.
HTH, but please post your results!