idle speed adjustment using foxwell nt 530

Hello there,
We have just tried to adjust the idle speed of our 3.0 Tdi Range rover Vogue using the 2003-2005 setting on a foxwell nt 530 scanner. After much fiddling around we managed to reduce it from 860 down to 820 and were happy, unfortunately after a road test which stayed at 820 we turned off, and the speed returned to 860, the scanner initially showed -40 which was great or at least much better than it originally was, does anyone know if there is a hidden save function on the foxwell, because for the life of me I can't find it!
Any help would be enormously appreciated because this is doing my head in!

Quick update, the save feature 'suddenly' popped up! Unfortunately so far it has only saved a 0.2 rpm reduction and deosn't want to go lower. THe unit states it will only adjust between 7.5 and 8.5 I would be really happy if I can gert it down to 7.5 but that seems as if it will require a bit of fiddling and NOT attempting to do it in plus 30 degrees! Shall have another go tomorrow when the heat is a bit lower and report back.

nevillen said:

Quick update, the save feature 'suddenly' popped up! Unfortunately so far it has only saved a 0.2 rpm reduction and deosn't want to go lower. THe unit states it will only adjust between 7.5 and 8.5 I would be really happy if I can gert it down to 7.5 but that seems as if it will require a bit of fiddling and NOT attempting to do it in plus 30 degrees! Shall have another go tomorrow when the heat is a bit lower and report back.

Click to expand...

Are you sure the Tacho in the car is accurate? Can you display actual rpm on the Foxwell as a check?

yep it shows rpm but I think I need to investigate the tacho possibility as well, especially as I have 275x65x18 tyres fitted I think they 'mess' with the system!

Can i ask why your trying to lower the idle?

Hi thee, because it is too high, I think it should be around 760. I spend half the week in traffic so it will make a big difference in diesel consumption. Once I am back in the country it doesn't matter.

nevillen said:

yep it shows rpm but I think I need to investigate the tacho possibility as well, especially as I have 275x65x18 tyres fitted I think they 'mess' with the system!

Click to expand...

I can see different radius tyres affecting road speed but not rpm.

The fuelling for cold engine is probably different to a hot one. Once at temperature it might drop back down.

nevillen said:

Hi thee, because it is too high, I think it should be around 760. I spend half the week in traffic so it will make a big difference in diesel consumption. Once I am back in the country it doesn't matter.

Click to expand...

Check the engine temperature sensor reading, if the ECU thinks the engine is not up to temperature, the revs may stay high.

Thanks for that Data, that was next up on my check list and I think will probably be the actual cause. Will need to replace ECU probably but I will disconnect it and give it a good blast with contact cleaner first. That is after I have got the old girl passed her MOT which she failed on a couple of weeping CV gaiters...as you know life is never simple with an old RR, but we are suckers for punishment and when they are fun they are really fun! Thanks for your help as always