v8 3.9 efi mechanics help wanted

Tried everything i can, and people i know but i cant get the bloody thing sorted. Its all ready to go but i cant sort the erratic idling out.It starts great and runs great but it ticks over at 1k then as it gets warm during driving it, which it does fine, when you take yr foot off of the throttle the revs will drop real slow but stay at 1500rpm, blip the throrrle and it'll go up quick but drop slowly. Sometimes it'll slowly go back to 1k rpm and others it'll stay at 1500. Had one trip the other day and it wouldnt drop to below 2000rpm. Wel thats no good for greenlaning. Tried a new stepper/idle valve. if i unplug the maf or afm whatever its called and it conks out, which i think means its working, all vacuum pipes seem ok.
Vehicle is a 1994 disco1, which also has lpg as well but the idle is the same on petrol and lpg.
Somebody has said perhaps its an inlet manifold leak, but im mechanically thick so i need help, will pay well,just want to get it sorted so i can join the essex green lane peeps. At the mo im just getting fed up

So if anybody if up to scratch on these please get in touch as i want it sorted asap, thanks

When you it say wouldn't drop below 2000 rpm do you mean that it stuck there or it wouldn't keep running below that?

Return spring on throttle ?

Dr_evil said:

Return spring on throttle ?

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I'm thick Doc, as you know. That's one of the reasons I asked my question. I'm in my own dull way trying to find out if it may be a mechanical or electrical problem. Because when my 4.2 went boobies up it exhibited problems running below 1500 rpms. If I could feather it from idle to those rpms, which was difficult, it would run all day. After chasing my tail (of this you are familiar) it turned out that I had a dodgy coil.

Without a response from the OP I'm afraid it will be difficult to help much. Not that I've ever really been that helpful before.

it runs lovely at that 2000rpm. it doesnt conk out, the revs just stay at 2000rpm. drive off, drived lovely , take foot off of throttle and it may drop to 1000rpm or it may just drop to 2000rpm. but when it does drop its real slow.
Throttle springs are fine
oh and im in north essex if theres any local clever bods

Mate my guess is as good as if not worse than yours I'm just naming things that might stop the idle from returning to the original place

I'm only putting some ideas out there but I've come across problems "like this" before and it's been one of the following
Idle valve faulty or sticking sometimes cleaning them out with some carb cleaner works
Throttle body needs cleaning out again with carb cleaner the flap and air screw ( if its removable )
Or there's an air leak in the intake side of the system
But that's only going on what you said but they are all easy to check and do so worth a go
Or being a land rover it could be something expensive that takes you years to sort out

Did it just start doing it or has it been played with?

Check the throttle pot.
Remove plenum and ram housing and clean thoroughly with carb cleaner, then check/set throttle disc, re-assemble ensure there are no air leaks. Remove and clean stepper and check operation.

Assuming it will fire up, get engine just warm then check/set base idle. Reconnect air bypass pipe, disconnect ecu to re-set, then plug everything back in and hopefully all will be well.

Check ignition timing and operation of mechanical and vacuum advance.