cappers

cappers

Well-Known Member
Disco 3.5V8 hotwire 14CUX + auto in a 90.

Recently the idle has been not been returning to base level (~700rpm) on lifting my foot off the accelerator and in neutral but hovering about 1000. Looking at the linkage it seems slack and I can press the ?throttle lever (red circle in first photo) back a couple of mm further and it returns to 700. So I need to tighten the cable a bit (2nd photo) but don't know how. Do I slacken the nut at the end pull the cable tight until the return is fully home then retighten the nut?
Thanks in advance.
IMG_2604.JPGIMG_2605.JPG
 
If there's lack in the cable but the butterfly doesn't fully return, then either it or the linkage is sticking somewhere
 
Thanks @kermit_rr
Linkage seems ok, spring and assembly cleaned with carb cleaner.
It's just when off the accelerator the bit in the upper red circle where the cable is attached doesn't go home fully; pulling the cable in the 2nd picture pulls it fully home (as does lifting the accelerator peal with my toes).

Does loosening the nut arrowed allow the cable to tighten?
279378-80a6f49c8b35fc3574ed75fac16b10ff.jpg
 
cappers said:
Thanks @kermit_rr
Linkage seems ok, spring and assembly cleaned with carb cleaner.
It's just when off the accelerator the bit in the upper red circle where the cable is attached doesn't go home fully; pulling the cable in the 2nd picture pulls it fully home (as does lifting the accelerator peal with my toes).

Does loosening the nut arrowed allow the cable to tighten?
View attachment 287697
Click to expand...
I think you need to tighten the nut on the top one, so there is less slack between the two cables.
And if adjustment doesn't work, a new spring can't do any harm.
 
The idle control valve looks after the idle rpm, and adjusts it
depending the load placed on the engine, not the length of the throttle cable.
Other things such as a simple blocked crankcase breather Can increase the idle rpm.
 
@discool
OK, I replaced the idle control valve as the original was playing up and since then the idle has been steady and correct.

However the cable I am referring to is the return cable which is slack and pulling it tight by hand closes the throttle to the stop and the revs return to base idle. The cable isn't closing the throttle fully but does when I tension it so just need to know how.
The resistance and voltages for the idle valve, TPS and AFM are in range and there are no detectable air leaks.
Haven't checked the crankcase breather but as I say I think this is a mechanical issue in that the butterfly isn't fully closing with a slack cable.
 
cappers said:
@discool
OK, I the idle control valve as the original was playing up and since then the idle has been steady and

However the cable I am referring to is the return cable which is slack and pulling it tight by hand closes the throttle to the stop and the revs return to base idle. The cable isn't closing the throttle fully but does when I tension it so just need to know how.
The resistance and voltages for the idle valve, TPS and AFM are in range and there are no detectable air leaks.
Haven't checked the crankcase breather but as I say I think this is a mechanical issue in that the butterfly isn'
Click to expand...
Ok so, ”return cable“ I haven‘t a clue on that one.
My 3.5 and now a 3.9 doesn’t have one, both are autos so there’s the throttle connected to the throttle stop, there’s an adjustment wheel for that, also connected is a kick down cable as its an auto and that has the locknuts as the means of adjustment.
All as you have already found out 😀
 
I'm lost, the diagram above is different to my setup?!

To recap (and I'm not sure of the correct terminology)... the bit in the top circle (throttle stop?) isn't going all the way back when off the accelerator so revs are about 900-1000. Pushing it shut or lifting the accelerator pedal with my foot or pulling on the cable in the lower circle closes it fully and the revs go back to irma ~700.
Adjusting the cable with the rubber boot (kick down?) doesn't pull the lever back home but tightening the other cable does.
Confused. Been trawling the net, my laptop and bookshelves for the appropriate diagram but no joy. I tlloks like the set up on my old 1990 RRC 3.5 auto if that helps.

IMG_2604.JPG

Pouring with rain so will have to wait until another day.
 
The cable with the silver crimp bit on it is the kickdown cable & needs adjusting as per the above or you will have issues with the operation of the kickdown.
The cable with the rubber boot thing is the throttle cable.

Remove the rubber hose from the front of the plenum chamber, prop open the throttle butterfly & clean the area where the butterfly closes as a build up of dirt can stop the butterfly closing properly.

On my own 3.5EFi Range Rover the plenum breather passageway was blocked. Remove the hose that goes from the breather on the r/hand rocker cover to the front of the plenum.
Prop open the butterfly & put clean lintfree rag into the plenum past the butterfly.
Use aerosol carb cleaner to blast out the passageway, it will come out of a hole on the front inside of the plenum housing just behind the butterfly & if you've got it right be absorbed by the rag.
Mine was blocked solid - causing the crankcase to pressurise resulting in oil leaks from all sorts of interesting places - & needed a poking out to clear it.
 
@Ratae Many thanks, now I know which cable is which :rolleyes:

The kick down is working fine so I'll not fiddle with that but I'll adjust the throttle cable tension to try and close it fully; at present there's about 2mm left to be closed.
I'll give the plenum breather passageway a good clean too.
 
Is there a return spring fitted to the accelerator pedal ?
ETC6949 is the disco item if not.

Also when cleaning the breather hose unscrew the flame trap and soak in petrol to clean.
 
I wonder if it's worth removing the throttle cable from the car & seeing if its operation is smooth?
Possibly hang it up & allow some light oil to run down inside - much the same way as oiling motorbike cables.
 
Quick look through LRcat shows the linkage on the V8 EFi Defender looks like yours.
Are all the springs in the diagram on yours?

Lrcat

new.lrcat.com

ETA. The hose in your pic looks like it's got a lot of tape wrapped round the end. Is that hose nice & tight & not allowing air in?
On mine the hose from the plenum to the extra air valve split at the end & so much unmetered air was going into the plenum it wouldn't run on petrol. Bit of an issue as I was on the car park at Pitsford having had the day fishing, it was getting dark & the staff wanted to lock the gates!
Fortunately it ran well enough on LPG to get me home.
I'd replaced the previous one with this which was new-old-stock & it had obviously not aged well on the shelf!
 
Last edited:
Thanks, I did notice the end of the plenum hose and will check its integrity later; weird, only really 'saw' it in the photo.
 
Slackened the throttle cable a couple of turns and the sprung lever went all the way home to the stop, then tensioned it so that when off the accelerator it just met the stop, and the idle is now steady again at ~700. So just an overtightened cable not allowing the throttle to close fully.

Checked all the plenum hoses for cleanliness and integrity and seems ok, the one in the picture above which looks looks its been wrapped is secure and a spray of quick start didn't change engine behaviour. I cleaned the throttle butterfly etc the other week and with a new idle air valve stepper motor and the adjusted cable all is sweet again.

Thanks all for the advice.
 
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