Having eventually wrestled the Discovery key from my daughter (its her daily driver) I set out on a drive to warm the auto box oil up before a drain and change. As usual, the drive threw up a few more issues that need looking at, but I'm getting used to that now.
When we first bought it a couple of months ago, I plugged in my Foxwell NT640 and one of the error codes it showed was a "driver demand 2" error. We had a number of other problems to sort out so this never got looked at. The only noticeable thing when driving was that you seem to have to push the throttle down quite a lot to get it moving. Boot it and it goes fine, its like the first 30% of the travel revs the engine but gives little power. But we/she's lived with it.
On the drive this morning I noticed it hesitated a few times, like it missed a couple of times. The temp gauge also read low, until it suddenly shot up to the usual middle position - not slowly like an airlock, but immediately like an electrical fault. Soon (a few miles) after this the EML light came on, the green M/S lights came on and I had no throttle - the engine ticked over fine though ! I turned it off, turned it back on, all the warning lights went off and it drove faultlessly. Got it home, did the oil change, drove it again and noticed it hesitated a couple of times again (but no more warning light dramas). I plugged in the Foxwell and the only engine fault logged was the same driver demand 2 error.
My simple brain says the accelerator assembly needs replacing. But then I did a bit of a search on here and some general googling and there seem to be a number of possibilities. What concerns me more is that a number of people have fitted a new accelerator assembly and its not been the issue. And looking at the price of a new accelerator/potentiometer assembly (LR030567 as its a 3A..... chassis number) I don't want to chuck her money at that if its actually something else.
What I could not find was some clear advice on how to test the existing accelerator assembly to be sure its actually faulty. My Foxwell shows the live data for the accelerator, but I don't know what values I should be looking for, or is there a better way to test it ?

See attachment but the code corroborated with the behaviour makes the TPS very suspect, you can buy known good SH one guaranteed from a 100% reliable supplier:
Discovery 2 Parts
Quality Used and New Parts & Accessories

Call Paul on
01206 211623 - office
07828 278465
07760 955966
07840 428888

Thanks sierrafery, just taken the readings and have the following:

Pedal NOT pressed:
D1 0.73v
D2 4.30v
Supp 0.00v

Pedal Pressed to the floor:
D1 3.8v
D2 1.3v
Supp 10.00v (!!!!!!)

Interestingly, the Foxwell is not showing a D3. I think I will have to get a dedicated reader for the D2, especially as I quite like the idea of getting a Discovery 2 as well.
So the "pressed to the floor" readings look wrong, especially that supply voltage ?

strange...i've seen Foxwell NT510 LR in action and it was reliable compared with hawkeye so maybe try your tool on a well working D2 if you have the chance to make sure it's reliable and if it is better replace the TPS

I will try that if I can find one locally. I've also dropped them an email to see why its only reading 2 tracks when there are 3. Its the NT644 Pro, so it does "everything" in terms of diagnostics. I only ended up getting a GAP IID for my L322 because that lets me edit the CCF and play with suspension heights etc - diagnostically I can't see it does anything the NT644 doesn't do, so I had high hopes for it on the Discovery.
I also contacted Paul by the way - what a gent, and so close to my home town ! He's sorting out a replacement assembly, sensibly priced

The D2 could have been fitted with either a 2 track TPS or a 3 track type. It's VIN dependant. Each TPS is a potentiometer, much like an old fashioned volume control. With age the actual track, a "thick film" variable resistor can become scratched or dirty, much like that old volume control can become noisy.
Unfortunately the two Throttle Position Sensors types are not interchangeable. From VIN 297137 should be three track types and before that should be two track.
This from the pages of RAVE:-

It's only about a setting made with tester not about physical setup these days cos only 3 track TPSs are available which can be set to 2 track with tester...if we speak about new part of course

Thanks, that's helped a lot. The readings I took seem OK at idle, maybe a bit out at wide open. But the 10v supply I'm seeing is strange, and not sure why no track 3. There was an outstanding software update for the NT which I've now loaded, so I'll try it again this evening and see if it changes anything. But I'm more convinced its the potentiometer now.

What I forgot to mention in the original post is that when I initially started the vehicle and reversed it down the drive, when I put it in neutral the engine revs sat at about 1500, just like a sticky cable (if it had one !!). I blipped the throttle a few times but it made no difference, turned it off and back on - idled normally again.

A replacement is winging its way to me for tomorrow so I'll see if that improves the situation. Thanks again, you've been a great help !

The replacement pedal assembly arrived this afternoon so as soon as my daughter got back from work I pounced on the car and replaced the old pedal. Not a difficult job if you are double jointed ! Anyway, hooked it up to the NT and no fault codes anymore. Took it for a run, much more responsive - very much like I remembered my TD5 from 17 years ago. I've got a list of other bits to look at tomorrow, including fitting an EGR delete kit, so will hook it up again to make certain.

Thanks for the information and help sierrafery

Fingers crossed m8....let's hope that this particular fault was cured